156 PROCEEDINGS OF THE MALACOLOUICAX SOCIETY. 



terminal one being a little narrower ; and the exposed portions of 

 valves v to viii are smaller than that of valve iii. In C. Gunnii 

 and C. striatus, valves iii to viii are of about equal width, and the 

 tegmentum does not vary noticeably in size or shape from the fourth to 

 the eighth valves. 



C. larvmformis was taken by Mr. Eliot at Apia, Samoan Is., 

 a locality not hitherto recorded for the species. 



3. Cryptoplax Gunnii (Reeve). PI. XV, Figs. 17-19, 24-26. 



This form was considered a vai'iety of C. striatus by Mr. Smith, 1 

 an opinion in which I formerly acquiesced. The study of numerous 

 well-preserved alcoholic specimens received from Mr. Bednall, how- 

 ever, now convinces me that C. Gunnii is entitled to specific rank. 

 Compared with C. striatus, the valves are decidedly narrower and 

 more coarsely sculptured ; the niucro of valve viii is less posterior ; 

 the posterior insertion-plate is vertical, with only a very slight upward 

 wave or sinus behind, and the whole cavity of valve viii is visible 

 when viewed directly from below. In C. striatus (PI. XV, 

 Tigs. 20-23) the valves are wider and more finely sculptured, the 

 niucro of valve viii is produced backward in adults, the posterior 

 insertion - plate slopes forward, is shorter and has a distinct sinus 

 behind, and viewed from below, conceals the posterior end of the 

 valve-cavity, until in quite old individuals this is filled up 



The valves in C. Gunnii are also far more widely separated, valves 

 i to iii only being in contact; valve iv is but shortly removed, the 

 others quite widely separated, the greatest space lying between valves 

 v and vi ; vi and vii being nearly as widely separated. 



The body is more vermiform, less broadly flattened beneath, and 

 less depressed. In individuals with valves of the same size, the body 

 of C. Gunnii is half as long again as that of C. striatus ; and the 

 integument bears wholly different spicular armature. 



C. striatus bristles with a dense covering of short, stiff, acicular 

 spicules, directed slightly forward, with an under-coat of shorter 

 spicules, 2 while in C. Gunnii there is a rather scant clothing of 

 minute, very short, stout, pointed spicules, with larger ones sparsely 

 scattered among them (PL XV, Fig. 25, x 30), or wanting. The 

 spicules are reddish-brown in places, elsewhere white, thus producing 

 the marbled colour-pattern of the animal. 



The young of C. Gunnii differs from the adult in the approximation 

 of all the valves, and in retaining more of the longer, white spicules, 

 sparsely scattered over the surface (PI. XV, Fig. 24, X 30). Both 

 of these characters point to ancestors with more the organization of 

 the genus Choneplax. The form of the tail valve does not differ from 

 that of the adult. 



1 Zool. Coll. H.M.S. " Alert," p. 85. 



2 See Manual of Conchology, vol. xv, pi. xi, fig. 37. 



