No. 186.] 29 



Genus Rhynchospira (n. g.). 



[ Gr. Qvyxos, rostrum j GTteiQa, spira : in allusion to its similarity in form 

 to Rrtnchonella, and having internal spires.] 



Terebratula and Wiynchonella of authors. 

 Waldheimia : Hall, 1856. 



Trematospira, Subgenus Khynchospira : Hall, 1857. 

 Rhynchospira : Hall, 1858. 



Shell longitudinally ovate or subglobose, more or less gibbous, 

 acute or obtuse at the apex. Valves subequally convex; mesial 

 fold not strongly defined, one, two, or more smaller plications 

 usually marking tlie centre of each valve : beak of the ventral 

 valve perforate, the perforation generally well defined, the lower 

 formed by a deltidium which separates it from the umbo of the 

 opposite valve. 



Surface radiatingly plicate or striate : shell-structure punctate or 

 striato-punctate 1 



Valves articulating by teeth and sockets; the crura supporting two 

 conical spires, which occupy the greater part of the cavity of the 

 two valves. The cardinal process of the dorsal valve is a broad 

 subemarginate plate, spreading laterally and a little recurved at 

 its basal margins, where it is clasped by the teeth of the opposite 

 valve, and extends beneath the deltidium, lying close against the 

 inner surface of that part of the ventral valve. 



The mode of articulation, as now determined, is very similar to that of 

 NucLEOSPiRA ; but the cardinal process is proportionally shorter and 

 emarginate at the extremity, the perforation of the beak large and distinct, 

 while the form is different and the exterior surface plicate or striate, and 

 not punctate as in that genus. 



The form of the species is not unlike Rkynckonella, but usually more 

 symmetrically rounded, and with less distinct mesial sinuosities. In these 

 characters they resemble Waldheimia, to which genus I had originally 

 referred them until the discovery of the internal spires. 



Several of these shells bear a close resemblance, both in the general form 

 and in the interior spires, to Retzia ; but the dorsal valve never presents 

 the straight extended hinge-line, nor the ventral valve the short area, 

 common to the cj,rboniferous species of that genus. 



From the external characters of the species referred by me to Atrypa 

 aprinis, Palaeontol. New- York, Vol. ii, pa. 280, pi. 57, f. 7 {^= Terebra- 

 tula aprinis, M. V. K. Geol. Russia and the Ural Mountains, Vol. ii, 

 pa. 90, pi. X, f. 10), I infer that it belongs to this genus. 



