Co BULI.EIIN ()F THE LABORATORIES 



greatest length 31 mm Found at Moot's run, four miles west of Gran- 

 ville, in nodules at the very bottom. 



Promacra i?) trimcafus. sp. n. 

 (Plate III, Fig. 30.) 



Without absolute certainty that this species can be properly re- 

 ferred to Promacra, it remains certain that a very peculiar species ex- 

 ists with a general resemblance externally to the assemblage so desig- 

 nated. Our specimen is incomplete and doubtless distorted, though 

 the peculiarities thought to be due to pressure may be inherent. Shell 

 elongate, produced anteriorly; beaks in front of or near the middle ; 

 strongly convex (in our specimen the transverse section is broadly cor- 

 date.) Dorsal margin in front of the beak straight; hinge extending 

 a short distance behind,the beak ; posterior m ngin very oblique, meet- 

 ing the nearly straight ventr.il mirgin at a very acute angle, at or near 

 the lowest part of the shell ; (anterior extremity not seen); post um- 

 bonal ridg'- very strong, acute ; plane of the jj.^st umbonal slope at 

 right angles to the sides of the shell, plane or somewhat concave, giv- 

 ing the shell a curious truncate appearance ; surface marked by strong 

 irregular furrows and strias, which in passing over the post umbonal 

 ridge make a very acute angle ; beaks incurved to the plane of hinge; 

 shell gaping widely behind, apparently closed or nearly so anteriorly. 

 Allowing for all probable distortion the shell seems distinct from all 

 others. It could not have been so extended anteriorly as F. andrewst, 

 nor as strongly marked as P. Jiasuius, though some indications of the 

 radiating stride of that species, which ours most resembles, can be 

 seen. 



The three known species are all from the same relative horizon. 

 P. missouriensis, from the sub-carboniferous rocks of Missouri, P. 

 nasutus, from Choteau limestone of the same state, and also in Bel- 

 gium, while P. andrewsi was found by Meek, in the Waverly group 

 of Ohio. 



LriopferUi ortofii, '^p- "• 



(Plate VII, Fig. i.) 



wShell of medium size, triangularly ovate to subrhomboidal ; body 



