22 PROCEEDINGS OF TIIE WALACOLOGICAL SOCIETY. 



that " Nothing of the sort or in the least approacliing it has ever been 

 described" ; but this statement is not quite accurate, since it has long 

 been knoAvn both in Galeomma ^ and Scintilla ^ that the valves Avere to 

 a large extent covered by a reflection of the mantle. IJoth genera 

 further resemble Ephippodonta in the fact that their reflected mantle 

 is beset with a series of papillae. 



This reflected layer of the mantle is, I believe, concerned in the 

 thickening of the shell, at any rate of the spines that exhibit a series 

 of superficial lamella?, which appear to have been recently deposited, 

 and which are quite independent of the regular horizontal lamella3 of 

 the shell (Fig. 18). 



I do not think that the internal character of the valves in 

 Ephippodonta and Chlamydoeoncha is due to any phylo genetic connec- 

 tion between the two, as the other points in their anatomy differ so 

 widely, but rather that this feature has arisen independently in both. 

 On the other hand the partial enclosure of the shells of Galeomma and 

 Scintilla in all probability represents a stage in the evolution of the 

 condition seen in Epliippodonta, since these three genera are un- 

 doubtedly closely related to one another. 



The Lahial Palps : — Two pairs of labial palps are present as in 

 Galeomma ; the outer or anterior pair are small triangular structures, 

 the fi'ce angle being roughly 90° (Figs. 2 and 8, Ip^, Ip'^). They are 

 situated on either side of the mouth, their bases being attached between 

 anterior adductor and the pedal protractor, slightly overlapping both. 

 The posterior pair are very small and completely hidden under the 

 larger anterior pair. The anterior free borders of the two mantle 

 folds are slightly inturned (retracted) and developed in sucb a way as 

 to roughly suggest an anterior pair of palps ; these probably form the 

 funnel-like structure that Tate speaks of in the live specimen. 



The Mantle cavity : — The branchial (infra-branchial) chamber (Figs. 

 12 to 15, i.e.), which is almost filled up in the contracted state by the 

 gills and body, is widely open below for about three-quarters of its 

 length. The posterior fourth of this cavity is closed below by the 

 fusion of the ventral edges of the mantle and ends blindly in two 

 coecal diverticula (Fig. 15, h.c), which are separated from the 

 supra-branchial chamber by the union of the two outer gill-lamellae 

 and by a horizontal muscular ingrowth of the mantle. During life 

 this cavity must be widely open, so much so that the gills and the 

 body must project freely. 



The supra-branchial (anal) chamber (Figs. 12 to 15, sp.b.c.) receives 

 the opening of the rectum, also the paired genital and excretory 

 orifices, it is single behind and communicates with the exterior by 

 the small exhalcnt siphon ; anteriorly the single chamber becomes 

 divided into three by the union of the inner lamella of the outer and 

 the outer lamella of the inner gill (point of origin of the gill) with the 

 body wall. Still further forward Ave find the middle portion of this 

 cavity becoming again sub-diAided by the intervention of the posterior 



' Jeffreys, Brit. Conch, v., p. 176, 1869. 



^ Sur le genre Scintilla, Par. G. P. Deshayes, Proc. Zool. Soc. 1855, p. 171. 



