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Isidora tabulata, Gould (1848), sp.
Physa tabulata, Gould, Proc. Boston Soc. Nat. Hist., vol. ii. (1848), p. 214; U.S. Expl. Exp., vol. xii., p. 116, figs. 136 a, b. Physa tabulata, v. Martens, Crit. List N.Z. Moll. (1873), p. 15. Physa tabulata, Hutton, Man. N.Z. Moll. (1880), p. 30. Aplexa tabulata, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus tabulatus, Hutton, Trans. N.Z. Inst., vol. xvii. (1885), p. 57. Physa tabulata, A. H. Cooke, P.Z.S. (1889), pp. 139, 140, fig. 4 (radula). Bulinus tabulatus, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii. (1893), p. 627. Bullinus tabulatus, Suter, Journ. de Conch., vol. xli. (1894), p. 233.
Fig. 1
The diagnosis is to be found in Hutton's Manual. Fig. 1 represents the species after a copy from Reeve (Conch. Icon., vol. xix., Physa, fig. 17b), kindly supplied with several others by Mr. Hedley. Taken from the figure the dimensions are—Shell: length, 22 mm.; breadth, 16 mm. Aperture: length, 12 mm.; breadth, 8 mm. I think it to be a most useful thing to establish the following rationis to help in separating the various forms: i. Ratio between breadth and length of shell = 1: 1.4; ii. ratio between breadth and length of aperture = 1: 1.5; iii. ratio between length of aperture and length of shell = 1: 1.8. Hereafter I shall designate these rationis simply by i., ii., iii.
Hob. A mountain-stream, Bay of Islands (Drayton).
Type in the U.S. Nat. Museum, Washington.
I have not seen this species.
Isidora tabulata, Gould, subsp. moesta, H. Adams (1861), subsp. Physa moesta, H. Adams, P.Z.S. (1861), p. 144. Physa coromandelica, Dunker, Malac. Blätter (1862), p. 150. Physa moesta, Hutton, Man. N.Z. Moll. (1880), p. 31. Aplexa moesta, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus moesta, Hutton, Trans. N.Z. Inst., vol. xvii., p. 57, pl. xii., fig. 12 (dentition). Bulinus moesta et coromandelica, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., pp. 627, 628. Bullinus moesta et coromandelica, Suter, Journ. de Conch., vol. xli., p. 233.
The very short diagnosis is fortunately supplemented by a figure in Reeve's Conch. Icon., fig. 32, the outlines of which I here reproduce (fig. 2). The dimensions, taken from the figure, are—Shell: length, 17 mm.; breadth, 11 mm. Aperture: length, 10 mm.; breadth, 5 mm. The proportions are: i. = 1: 1.5; ii. = 1: 2; iii. = 1: 1.7.
Fig. 2.
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I have examined and measured specimens in my collection from the following localities:—
(1.) Ditch near Lake Takapuna, Auckland. The specimens are fuscous, with a ferrugineous coating, shouldered, larger and more slender than the type. Two specimens measured gave length of shell 15 mm. and 17 mm., breadth 9 mm.; and the mean proportions were found to be—i. = 1: 1.8; ii. = 1: 2; iii. = 1: 1.7.
(2.) From Lake Takapuna, Auckland. Two specimens, dark-brown, strongly carinated, larger and a little less ventricose than the type. Shell: length, 12–15½ mm.; breadth, 7–9 mm. Mean rationis—i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.5.
I first tried to uphold I. coromandelica, Dunker, as a separate subspecies of I. tabulata, as the specimens of the above three localities approach the ratio between breadth and length of shell of I. coromandelica, which is 1: 2, but I soon found out that all intermediate forms, from the elongated coromandelica to the more ventricose moesta, are met with, and, as there seems to be no other character available to distingusih the two, I thought it advisable to make the former a synonym of the latter.
(3.) Wanganui (no exact locality). One adult and two not quite full-grown specimens were measured. The adult had—length, 17 mm.; breadth, 10 mm. All specimens are shouldered. The mean proportions are—i. = 1: 1.6; ii. = 1: 2.1; iii. = 1: 1.4.
(4.) Fresh-water stream, Parua Bay, Whangarei. All specimens are blackish-brown, two are distinctly shouldered, the other has smooth whorls. The columellar fold is very distinct. Three shells showed the length to vary from 9–15 mm., the breadth from 5½–9½ mm. The mean proportions are—1 = 1: 1.7; ii. = 1: 1.9; iii. = 1: 1.6.
(5.) Waikato River, near Huntly. Shells of good size, chestnut-colour, some with a ferrugineous coating; young specimens are strongly carinated, in adult specimens the carina is reduced to a slight angulation on the last whorl. Columella strongly twisted. Four shells were measured, the length being 12–15 mm.; breadth, 8–11 mm. The mean proportions were—i. = 1: 1.4; ii. = 1: 1.9; iii. = 1: 1.5.
(6.) Chatham Islands. One specimen only, of yellowish-brown colour, with four shouldered whorls. This is a slender form. Length, 8 mm.; breadth, 4½ mm. Rationis—1 = 1: 1.8; ii. = 1: 2; iii. = 1: 1.6.
The result of measuring twenty-eight specimens is the following: Ratio i.—variability, 1: 1.4 to 1: 1.8; mean, 1: 1.65. Ratio ii.—variability, 1: 1.9 to 1: 2.3; mean, 1: 2. Ratio iii.—variability, 1: 1.4 to 1: 1.7; mean, 1: 1.5. It shows that the shells of this subspecies are a little more slender and the spire
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is somewhat higher in proportion to the length of the aperture than in the type specimen figured.
Type in the British Museum (?).