180 PROCEEDINGS OF THE ACADEMY OF 



of the mesial fold and sinus. Ventral valve more gibbous than 

 the other, and strongly arched from beak to front; beak very 

 prominent in the adult, always point and distinctly curved back- 

 ward over the hinge; cardinal area moderate, well defined, ex- 

 tending to the extremities of the hinge, directed backward and 

 strongly curved with the beak ; foi'amen slightly wider at the 

 hinge than its height, open nearly or quite to the apex, and pro- 

 vided with a distinct marginal furrow on each side ; mesial sinus 

 angular, commencing small at the beak, but widening and deepen- 

 ing very rapidly to the front, where it is very profound, and ter- 

 minates in a strongly curved triangular projection that fits into a 

 corresponding sinus in the margin of the other valve; surface cos- 

 tated as in the other valve, the costse in the sinus being smaller 

 than those on the lateral slopes; fine, rather obscure undulating 

 stride, and near the front and lateral margins a few stronger marks 

 of growth traverse the valves parallel to the free margins ; while 

 numerous small, rather scattering but regularly disposed granules, . 

 apparently the remaining bases of minute spines, may be seen on 

 the whole surface of w^ell-preserved specimens ; Avhich also some- 

 times show traces of extremely minute radiating stria. 



Length of a large gibbous example, 1 inch; breadth, 0.88 inch; 

 convexity, 0.82 inch; length of hinge, 0.51 inch. Smaller speci- 

 mens are proportionally shorter, wider, and less convex, with a 

 lono-er hinge line. 



Small specimens of this species resemble somewhat the more 

 gibbous forms of S. cameratus, with a very short hinge line ; but 

 in the adult the shell becomes proportionally much more elongated 

 anteriorly, more gibbous, and has the beak of the ventral valve 

 so narrow and so much produced and incurved as to give the 

 shell the appearance of a Pentamerus. Its distinctly granular 

 and minutely striated surface, however, will always serve to dis- 

 tinguish even those specimens with the most extended hinge line 

 from any of the analogous gibbous varieties of S. caniarafus. Its 

 granular surface leads me to suspect that it may possibly be a 

 Spiriferina ; but as I have not been able to see any punctures in 

 the substance of the shell, it probably does not belong to that 

 group. Should a more careful examination reveal the punctate 

 structures, however, and the characteristic internal lamina, of 

 course the species will have to be called Spiriferina Texana. 



[August 15, 



