56 McMahon 8^ HiicUeston — 



rendered somewhat quadrate in appearance by a slight slipping 

 of the valves. The dorsal valve is shown with the very small 

 beak of the ventral valve just projecting beyond the hinge-line. 

 The radial costge are salient, rounded, and highly imbricated, especially 

 anteriorly (Fig. 5&). 



In Fig. 6 we have a larger but less well-preserved fossil, and 

 the original outline was probably less circular. This may be 

 regarded as more nearly approaching A, reticularis ; an enlargement, 

 however, would show the costse to be strongly imbricated and 

 almost squamose. The valves as a rule are moderately tumid, 

 the dorsal valve usually the most so. 



Fig. 4 is a good example of the var. squamosa, Sowerby. In this 

 case the circular outline is well shown, whilst the highly squamose 

 character of the anterior portion of the shell is obvious. 



Figs, la, b represent a perfectly circular and slightly globose 

 form of medium size with very large imbricated costse. This may 

 be compared with the var. Sinensis of Kayser, though specimens 

 from China would seem to have the dorsal valve less tumid. 



11. Atktpa, species or variety. (PL III, Figs. 8a-c.) 



This form is an exaggeration of the small circular variety of 

 Atrypa last described. Both valves are extremely tumid, so that 

 the shell is almost as globose as a ball. The only available specimen 

 is much abraded, but it is possible to perceive that the cost^ were 

 highly imbricate, and that there are indications of a shallow sinus 

 and slight mesial fold. 



12. Cf. Eenssl^ria stringiceps, F. Eomer. (PI. Ill, Figs. 9a-c.) 



Bensslceria stringiceps ?, F. Eomer: Brit. Dev. Brach., -p. 10, pi. iv, figs. 5-7. 



A single specimen, somewhat indifferently preserved in very 

 black limestone, bears great resemblance to the fossil figured by 

 Davidson under the above appellation. It is a terebratuloid shell, 

 with a beak apparently possessed of a circular foramen : shape 

 oblong, valves tumid, especially the dorsal valve. The dorsal 

 valve swells out rapidly from the hinge area ; the ventral valve 

 has a slight median ridge, increasing in sharpness towards the beak. 

 The valves are ornamented with strong radiating nodular costa, 

 about 20 in each valve. 



13. Ehynchonella, species. (PL III, Figs. lOa-c.) 



Shell transversely oblong ; length 18 mm., estimated width 28 mm. 

 Dorsal valve ventricose ; ventral valve inclined to be flat, and 

 provided with a wide, shallow sinus towards the anterior margin, 

 which is only slightly sinuous. From 30 to 35 medium-sized costas 

 increase regularly towards the anterior margin without interpolation. 



This is the only specimen in the collection which can be confidently 

 referred to Bhjnchonella. It is an average sort of form, which may 

 possibly have some relationship to B. parallelopipeda, Bronn (vide 

 Eichthofen's China, Bd. iv, p. 77, pi. viii, fig. 1). 



