154 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



keels and often some striae (PI. XIY, Fig. 11). There are no 

 discernible pores or pore-tufts and no marginal fringe. The lower 

 surface covered with far shorter, smaller scales than the upper. 



Foot wholly concealed in the ventral groove (in alcoholic examples), 

 narrow, but with flat sole and crenate edges. Gill row rather less 

 than one-fifth the total length of the animal. 



Length (of an alcoholic example) 55 to 60 mm. 



Hah. — Apia, Samoan Islands, collected in 1899 by Sir Charles Eliot, 

 H.M. Commissioner to Samoa, after whom the species is named. 

 Type No. 77,308 : Conch. Coll. Acad. Nat. Sci. Philadelphia. 



This is the most divergent of all the known species of Cryptoplax, 

 the valves being more reduced in size and more widely separated than 

 in any other. The bright spicules give the animal a silvery gleam, 

 Kke Chcetoderma. Apparently the Cryptoplacidae are developing 

 a stock parallel to the Aplacophora in their vermiform shape, loss 

 of valves as protective armour, and renewed predominance of spicules 

 for this purpose, and the posterior position of the gills. 



The dimensions in millimetres of the individual valves of the type 

 are as follows : — 



It will be noted that the articulamentum is smallest in valves 

 v and vi, but the tegmentum in valves iii and iv. In C. larvceformis 

 the two layers of the valve decrease together, and are smallest in 

 valve vi. In the latter species there is no conspicuous change in the 

 form of the sutural laminae between valves iii and viii, but in 

 C. Elioti these lamina? become abruptly short at valve v, continuing 

 so upon the subsequent valves. In the valves anterior to v, the 

 insertion-plates and sutural laminae are formed more as in all the 

 valves of C. larvceformis. The shortening of the articulamentum 

 of valves v-viii in C. Elioti indicates accelerated degeneration of the 

 valves in the posterior half of the body. 



The nearest ally of this species is C. Burrowi of E. A. Smith, 

 which has a posterior valve of the same shape, but its valves are far 

 less degenerate. 



2. Cryptoplax larvceformis (Burrow). PI. XIV, Figs. 12-16. 



The girdle in this species resembles that of C. Gunnii more than that 

 of any other. The valves of adults show distinctly senile features, 

 and the ontogeny has evidently been considerably ' accelerated.' 



In a young specimen (length in alcohol 35 mm.), valves ii to viii 

 show a well-defined dorsal area as a smooth median band ; on either 

 side of this are numerous riblets parallel with it. This condition 

 obtains until the tegmentum of valve viii is nearly 3 mm. long. In 



