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[Read before the Philosophical Institute of Canterbury, 18th December, 1918; received by Editor, 30th December, 1918; issued separately, 26th May, 1919.]
The genus Ceina was established in 1893 by Della Valle for the single species C. egregia (Chilton), which had been described in 1883 under the genus Nicea Nicolet, a genus now considered to be identical with Hyale H. Rathke. The species was placed under Nicea because it appeared in many respects to come near to Nicea rubra G. M. Thomson, N. fimbriata G. M. Thomson, and other species then referred to Nicea; but it was pointed out at the time that it differed in several important characters, and some points in the original description were left more or less doubtful. Stebbing in 1888 (p. 1712) mentioned the species, stating that its generic position was not quite free from doubt. In establishing the new
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genus Ceina, Della Valle gave a brief description which may be translated as follows: “Upper antennae a little longer than the peduncle of the lower. Second gnathopods of male chelate. Third uropods represented by peduncle without rami. Telson divided.” He pointed out that the species was deserving of further investigation, particularly with regard to both pairs of maxillae and to the terminal uropods. In this paper I endeavour to supply the information that Della Valle considered was necessary, and I regret that various circumstances have prevented its being supplied earlier.
In 1906 (p. 554), in his revision of the Amphipoda for Das Tierreich, Stebbing described the genus as follows: “Antenna 1 longer than peduncle of antenna 2. Maxillipeds, finger of palp broad, subtriangular. Gnathopod 1 in male and female and gnathopod 2 in female subchelate, small. Gnathopod 2 in male much larger, subchelate or (in maturity) chelate. Uropod 3 tubercular, without rami. Telson partially cleft.”
There are also one or two points not mentioned in this description owing to their having been previously undescribed which are worthy of being included in the generic description. Thus, in the mandibles the usual molar tubercle is quite absent, and appears to be represented or replaced by a peculiar lappet on the inner surface directed backwards towards the base of the appendage. In the first maxilla the palp is absent or very minute, as in most of the species of Orchestia; the outer lobe is of normal structure, but the inner lobe is very small, barely half as long as the outer, and without the usual two plumose setae. It thus differs from the character of this maxilla as laid down by Stebbing for the family Talitridae, where he says “maxilla 1, inner plate slender, tipped with 2 plumose setae”; Sars (1895, p. 21) also gives this as one of the characters of the family, and the diagnosis of the family will therefore need to be slightly modified to include the genus Ceina. The second maxilla and the maxillipeds are fairly normal; but the large chelate second gnathopod of the male is a distinctive feature, and the terminal uropods are peculiar, being represented only by a short tubercle, which probably is the modified peduncle without rami. In this last character Ceina differs markedly from Hyale and approaches the allied genus Chiltonia, where the terminal uropods are represented by a single joint.
The generic diagnosis and the synonymy of the species may be given as follows:—