articulamentum thick and broad, here and there narrowly ridged, slits corresponding with ray-ribs; median valves slits 1/1, posterior valve irregularly slit as in genus Notoplax.

Measurements.—Of spirit specimen, total length 42 mm., width 23 mm. of which the girdle occupies two-thirds, total length of body, i.e., foot and head, 33 mm. of which head occupies 5 mm., width of foot a bare 10 mm., width of head 8 mm., gills post-median, 20 gill-slits counted which commence 4 mm. in front of anal extremity and extend forward 17 mm.

Remarks.—Suter's excellent description compared with the foregoing will give some idea of the margin of variation but he was incorrect in stating that the girdle was almost naked with very few silvery hairs near the margin. I have not seen any marginal fringe and the apparent absence of spicules under a low power is misleading, for minute spicules are distributed all over. Suter was also quite unaware of the sub-obsolete hair-tufts; again, he was incorrect in stating that the teeth in the first seven valves are finely pectinated, because in the usual acceptance of the term as applied to the genus Tonicia they are not pectinated at all; a glance at the figure of Tonicia will at once show the difference; Suter's statement “with gills extending nearly the whole length of the foot” is hardly correct, as a reference to the within measurements will show that the gills are but little more than half the length of the foot.

I consider Pseudotonicia cuneata to be a specialized form belonging to the family Acanthochitonidae; and whereas in the subfamily Cryptoplacinae the slits of the anterior valve are reduced to 3, in this species they are reduced to 4. As this feature is persistent, it will seem advisable to erect for its reception a subfamily Pseudotonicinae, immediately following the subfamily Acanthochitoninae.

Addenda.—Since the completion of the paper Mr. Brookes informs me that he has obtained three additional examples of Pseudotonicia cuneata, in each of which the anterior valve possesses 5 rays with corresponding slits in the insertion-plate. It is quite evident that the reduction of slits in this valve to four is not constant, and I have therefore asked Mr. Brookes to correct letterpress making the description read “4 or 5 slits” and I take this opportunity of expressing grave doubts as to whether the existence of the “minute eye-dots” is, taken by itself, sufficient grounds to warrant the retention of the proposed new subfamily Pseudotonicinae; if not, then this genus will have to be relegated to a position under the subfamily Acanthochitoninae.

Habitat.—Brookes collected all his specimens in Tauranga Harbour, opposite the town, in three fathoms. The two damaged specimens referred to were obtained from the mooring chain, and the others from the spoil deposited by the dredge engaged in deepening the approach to the new wharf. Bottom of hard pumiceous formation. The original specimen described by Suter came from the Bay of Islands.

Acanthochiton thileniusi.

Acanthochites thileniusi Thiele, Rev. des Sys. der Chitonen, pp. 50–51, pl. 6, figs. 55–58, 1909.

Acanthochites tristis Iredale, Proc. Mal. Soc. Lon. vol. 9, pt. 3, p. 155, 1910, not of Rochebrune.

Acanthochites (Acanthochiton) bisulcatus Wissel, Zool. Jahrb. Systs., vol. 20, p. 614, pl. 21, figs. 28–29 (anatomy), only applies to examples from Tauranga; not of Pilsbry.

Acanthochites zealandicus thileniusi Ashby, “The Acanthoid Chitons of New Zealand,” Proc. Mal. Soc. Lon., vol. 17, pt. 1, pp. 13–14, pl. 4, figs. 5–7.

Introduction.—In the writer's paper “The Acanthoid Chitons of New Zealand” (l.c.), he gave an English translation of Thiele's description, and commented on points of difference between an example in his own collection that had originally been sent to him by the late Henry Suter, the data as to locality having been lost; it will therefore be unnecessary to reproduce that translation, only quoting the following comments.

“Thiele makes reference to longitudinal grooving in the dorsal areas, and this at first led me to conclude that his shell was conspecifie with the deeply-grooved shell hereinafter described under the name brookesi; a reference to Thiele's figure of the tail-valve entirely precludes such a possibility. Thiele also described A. zealandicus as having longitudinal grooving in the dorsal areas; I therefore conclude that in both cases his remark refers to sub-cutaneous lining, which so simulates grooving that its true character can only be determined by the use of a binocular microscope and lateral lighting.”

The rediscovery of A. thileniusi at the type locality by Brookes enables the question of the longitudinal grooving in the dorsal areas to be finally settled; he has given me two of his Tauranga specimens, and these show distinct longitudinal grooving in the dorsal areas, but the riblets are about half the width of the corresponding riblets in Brookesi Ashby, the grooving much shallower, and their structure when seen under a microscope quite distinct.

Comparison with Allied Forms.—Although I still consider thileniusi to belong to what I call the zealandicus section of the genus Acanthochiton, the very definite grooving and peculiar sculpture of the riblets of the dorsal areas justifies the erection of this species to full specific rank.

In thileniusi the dorsal area is a little narrower than in either zealandicus or doubtlessensis, but very similar to this area in brookesi; in both zealandicus and doubtlessensis longitudinal grooving in this area is absent, but present in thileniusi and brookesi; in the former the riblets are sinuate and rugose, the grooves between being very shallow, the riblets between the grooves varying in width from about 50 to 62 mmm.; in brookesi these riblets are not wavy and rugose but straight and comparatively smooth, and the grooves between much deeper; the width of these riblets varies from about 62 to 100 mmm.; the coarser riblets are formed by the confluence of two narrower ones and often show a shallow mid-groove.