56 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



The Bhynchonella cuneata has a nearly similar form, but has not the 

 punctate structure and internal spires,* though having a well-defined area 

 below the beak. 



These rhynchonelloid species, therefore, form a peculiar group, distin- 

 guished externally by the punctate texture ; but the area and foramen are 

 features common to the non-punctate forms. t • 



The Retzia ovalis (SANDBERGER),t though having internal spires, has a 

 non-punctate shell ; and in the specimens I possess, I am unable to find 

 any distinct area. It has a large cardinal process in the dorsal valve, quite 

 unlike anything in the B.ferita, and of a character totally different from 

 the American species of the type of R. serpentina. In general form and 

 surface characters, this species resembles Atrypa (LeptocceJia) planoconvexa 

 of the Clinton group of New-York, the hinge-structure of which, as I have 

 already indicated, difi'ers in some respects from the Leptoccelia of the 

 Oriskany sandstone. 



Among those species which I have included under the Glenus Tremato- 

 SPIRA, the T. cainura approaches in character to the group above mentioned; 

 but it has a much more extended hinge-line and a distinct mesial sinus, 

 with one or two smaller plications. "A similar form from Tennessee has the 

 sinus, with plications as on the sides. We have likewise a species in the 

 Hamilton group ( T. gibbosa), with simple plications and a well-defined 

 sinus. 



These species have all, however, a transverse diameter greater than the 

 longitudinal diameter ; which character is likewise true of Terebratula 

 salieri, now referred to the Genus Retzia. 



In Trematospira perforata and T. multistriata, the plications are several 

 times bifurcated, and there is a strong and well-defined mesial sinus and 

 fold. In neither of these do we know the existence of deltidial pieces. There 

 is a triangular notch or slit below the perforated beak ; and on each side of 

 this, a narrow flattened space. The Trematospira costata has the aspect of a 

 Spirifer, is nearly twice as wide as long, and has a well-defined mesial 

 sinus and fold. 



To include these species in the Genus Retzia, would require a consider- 

 able e^itension of the characters originally given to it ; nor does it appear 

 to me that such species as R.ferita can be naturally grouped with such as 

 Trematospira multistriata and T. costata of the Lower Helderberg group, 

 or T. gibbosa of the Hamilton group. 



The following illustrations will afford the means of comparison among 

 these different species. 



* The R. cuneata is cited in Murchison's Sihiria as Retzia; but in examining 

 European specimens of this species, as well as the American forms referred to the 

 same, I have not found either punctate structure or internal spires. 



t I have heretofore ( Thirteenth Report on the State Cabinet, pp.67 & 68) shown 

 that in old specimens of R. increbescens. there is a perforated beak, and a solid tri- 

 angular area below. 



^ Specimens received from Dr. Rominger. 



