202 



PROF. REYNOLDS AND MR. V AUG HAN ON THE [May I 904, 



Plicatula cloacina. 



sp. iiov., constructed 



from numerous 



fragments. 



Plicatula cloacina, sp. nov. (Text-fig. :3 & PL XVIII, fig. 5.) 



Upper v a 1 v e. — Largest dimension about 

 Fig. 3. — Diagram of 2" millimetres. 



Valve strongly convex, narrowing to- 

 wards the beak. 



Shell thin, and composed of slightly- 

 overlapping, concentric bands which have 

 free ragged edges. Fine, sharp, radial ribs 

 cross these bands at irregular intervals, and 

 end on the free edges in projecting points. 

 The outermost bands are ornamented with 

 fine, close, parallel, concentric, rounded 

 stria 3 . To the left of the valve, the radial 

 ribs and spines arc much more numerous 

 and strongly marked, several of the ribs 

 are continuous, and the spines closely 

 packed, short, and tubular. 



Lower valve very imperfectly known. 



The specimens all occur in the Bone- 

 Bed (hence the specific name). 



[Magnified 2 diameters.] 



Lima valoniensis. 



Fragmentary and crushed specimens are not uncommon at the 

 main Pecten-hovizon. 



Pecten valoniensis, Defr. (PL XVIII, figs. 2 & 2 a.) 



The general characters of this species are : — 



The byssus-valve is fiat, with a narrow beak-angle (80 c to 85 ), 

 and ribs usually in pairs. The larger valve is convex, with a broader 

 convex beak (beak-angle about 100), and ribs more equal, but 

 usuallv containing a few intercalated shorter ones. Concentric 

 lines of growth not forming erect scales on the ribs. 



The most striking characters are : the transversity of the valves, 

 and the absence of symmetry, characters which are especially marked 

 in the convex valve. 



This species was excellently figured by Dumortier (3) in his pis. ix 

 & x. Under the name of Pecten cloacinus, Quenstedt (2) gave two 

 figures, both of the convex valve. Both figures illustrate the trans- 

 versity of the species, but the larger figure is more symmetrical than 

 is usually the case, and the left wing seems to be erroneously drawn. 



A maximum in the upper part of the Lower Rhsetic (III) : see 

 p. 200. 



Avicula contorta, Portlock (6) [including Avicula solitaria, 

 Moore (1)]. 



Of the special characters shown by our specimens, we may note 

 the following : — The anterior convex portion of the large valve is 

 almost smooth, and this smoothness extends to some distance round 

 the lower margin in big specimens. Small specimens exactly 



