MOLLUSCA. 



BllACHIOPODA. 



GENUS ORTHIS, Dalman. 

 ORTHIS (sp. undt.) 



PI. 2, Fig. 5, and 5 a, b. c. 



Compare Orthis Michelini, L'Eveille (sp.). Davidson, Carb. Brach. Grt. Brit., 

 pi. 30, Figs. 6 to 11. 



SHELL small, suborbicular, or a little oval, the length being 

 greater than the breadth ; hinge-line very short, or less than one- 

 third the breadth of the valves, and not imparting any angularity 

 to the lateral margins. Valves nearly equal, without any mesial 

 depression. Ventral valve somewhat flattened in front, but more 

 convex than the other in the umbonal region ; beak prominent 

 and incurved ; area small, regularly arched ; foramen higher than 

 wide. Dorsal valve more regularly convex than the other, most 

 prominent between the middle and the cardinal margin; beak 

 rather prominent, but less so than that of the other valve, mode 

 rately incurved. Surface of both valves ornamented with fine 

 threadlike radiating striae, which increase by division and inter 

 calation; crossing these are a few distant, obscure, concentric 

 marks of growth. Striae of both valves showing the bases of 

 minute, scattering, hair-like, tubular spines. 



Length, 0.35 inch; breadth, 0.32 inch; convexity, 0.17 inch. 



This little shell seems to be an exact miniature of Orthis Michelini, L'Eveille, 

 excepting that its beaks are more prominent and arched than is common in that 



(10) 



