CONOCARDIUM ROSTRATUM. 453 



regard tliis opening to have permitted the protrusion of a very well-developed 

 foot. 



Those who hold that the rostrum is anterior think that it may have existed for 

 the passage of the byssus ; but I have shown that there is strong presumptive 

 evidence that the byssus was placed elsewhere. On looking directly into the 

 gaping extremity of the shell it will be noted that the opening is divided into two 

 parts, the upper of which is separated from the lower by a ridge. I consider that 

 the upper part was largely occupied by the anterior adductor muscle ; the lower 

 part of the opening narrows to a point, and its sides are marked with large, 

 distinct, short ribs, which become smaller and smoother as they pass backwards. 

 The shape and nature of this opening preclude the assumption that siphon-tubes 

 passed through it, which must have been the case if this were the posterior end, 

 for the posterior adductor scar is always superior to the siphons. The shell is 

 completely closed at the truncated end, the edges of each valve being furnished 

 with strong teeth and sockets ; so that no place is left for the protrusion of the 

 foot, which would be the case if it were the anterior end and the soft foot would 

 have to be drawn backwards and forwards over many sharp prominent inter- 

 locking teeth, and therefore be liable to considerable erosion. 



I have described the characters of the genus from specimens of G. Eerculeum, 

 de Koninck, because I happen to have obtained more perfect examples of this 

 species than any other. The original type is, of course, that species from which 

 Bronn described the genus. I have, too, given a much fuller and minute generic 

 description than has been my custom hitherto, because British specimens are 

 rarely met with showing the details of the interior to such au extent as obtains in 

 the specimens from Tournai. 



Fourteen species of Conocardium have been described from British Cai'- 

 boniferous rocks, the majority of which are retained ; but a few are undoubtedly 

 synonyms, and therefore must be dropped. De Koninck describes twenty-six 

 species from the Carboniferous rocks of Belgium, but I am of opinion that many 

 of these are different states of growth of species described under other names. 

 With the doubtful exception of C. fasiforme, all the British forms are to be found 

 in Belgium ; and in the case of this shell I think it possible that G. Herculeitm, de 

 Koninck, may be a somewhat local variety of this species. 



Conocardium hostratum, Martin, sp., 1809. Plate LI, figs. 6 — 9. 



CoNciiYLioLiTHUs (Aecites) eostkatus, Mar/ill, 1809. Petref. derbieusia, tab. 



xliv, fig. 6. 

 Caedium elongatum, Sow., 1812. Min. Concli., vol. i, p. 188, pi. ]xx.\ii, fig. 3. 



