178 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



the ligament, together with the peculiar positions of the muscles, di- 

 stinguish it from Astarte ; but I leave it in that genus till more is 

 known of it. 



Plate XXI. fig. 4 a. Exterior. 



Fig. 4 b. Dorsal view of the same specimen. 



Fig. 5. Cast of the interior of another specimen. 



AvicuLA Olisiponensis, n. s. Pl. XVIII. fig. 3. 



Subrhomboidal, elongated, slightly oblique, nearly equivalve, gib- 

 bose : the anterior side very steep, anterior wing small : posterior 

 side gradually sloping, with the posterior wing ill-defined : shell 

 marked anteriorly vdth distant subsquamose lines of growth, on the 

 posterior vring with waving folds, and on the middle portion with 

 several elevated rays, which rise near the ventral margin into sharp 

 ribs. 



Length 2 inches; breadth Ij; thickness 1 inch. 



In the upper beds of the hippurite limestone near Lisbon ; rare. 



Only one cast of this species has been seen with portions of the 

 shell adhering to it ; fragments of three sharp ribs remain near the 

 ventral margin, and it is possible that one or two more similar ribs 

 may be lost : these sharp, smooth ribs and the form of the shell are 

 sufficient to distinguish the species. 



Caprinula, D'Orbigny. 



I hoped to have received, before publishing this paper, that part of 

 M. d'Orbigny's * Paleontologie Fran9aise' in which the Caprinidce 

 are described, but unfortunately I have only seen the plates of these 

 shells without the text, and the notices which that author has previ- 

 ously published on the subject ; I am therefore forced to draw up a 

 description of this curious genus, which is necessarily less complete 

 than it would have been if I had had the advantage of seeing his views 

 of it fully explained. 



The Capi'inulce are bivalve shells of great irregularity of form, with 

 the valves very unequal ; the lower valve which was probably attached 

 when young is either curved or involute, the spire rarely exceed- 

 ing two whorls : the two valves seldom lie on the same plane. The 

 exterior is either smooth, wrinkled with concentric lines of growth or 

 longitudinally fluted, and the markings of the two valves frequently 

 diff"er in character, as is the case in several species of Biceras. The 

 interior of both valves is divided into two larger and several smaller 

 cavities by longitudinal plates which do not rise so high as the edge 

 of the valves, and which divided the body of the mollusk into several 

 lobes. In the upper valve of the species which I have seen, these plates 

 are very oblique and were formed anew from time to time, cutting off 

 the extremity of the cavity, which was abandoned. 



The walls of the shells of both valves are perforated throughout by 

 numerous longitudinal tubes, of unequal length and diameter, and 

 open at the edges of the valves ; these must have received thin, elon- 

 gated lobes of the mantle. It is this peculiarity which appears to 

 have led M. d'Orbigny to class the Caprinid<s in the family of i2w- 



