144 Annals of the Carnegie Museum. 



fore proposed the name Cleiothyridina and designated as the genotype 

 Athyris roissyi as figured by Davidson, in the " Monograph of Car- 

 boniferous Brachiopoda," PI. XVIII, fig. 8. (See Annals and Maga- 

 zine Natural History, Series 7, Vol. XVIII, p. 321, 1906.) 



Description. — The adult shell varies in outline from subcircular to 

 transversely elliptical. The sides and front of the shell are usually 

 somewhat straight, which gives the shell a rather quadrate form. The 

 valves are nearly equally convex, the pedicle valve being slightly the 

 deeper. The pedicle valve shows a narrow sinus or a flattened area in 

 nearly all specimens, but in a few this valve is uniformly convex. On 

 the brachial valve there is a low fold which is not defined at the sides 

 and can be seen only when looking at the front of the shell. The 

 beak of the pedicle valve is small and closely incurved, but the pedicle 

 opening remains clear throughout life, the pedicle continuing to 

 encroach upon the umbo as the beak becomes more incurved. 



The surface markings on the better preserved specimens are those 

 characteristic of the genus. The concentric lamellae are very 

 immerous and the spiniform extensions of their free margins are long 

 and slender. Partially exfoliated specimens show fine, interrupted 

 radial striae, and casts of the interior show very numerous radiating 

 vascular markings. 



The spirals of a single specimen have been developed. They were 

 replaced by hematite, while the interior of the shell was filled with 

 calcite, thus permitting the use of acid. Each of the cones was found 

 to taper rather rapidly outward and consisted of eleven turns of the flat 

 lamella. The lamella were not fimbriated as Davidson found those of 

 Athyris pectinifera Sowerby to be. Unfortunately the loop of this 

 specimen was so distorted that its form could not be made out. 



No other species of this genus are known from the Devonian, but 

 several species have been described from the Mississippian and Pennsyl- 

 vanian. The shell known as Cleiotliyris roissyi L'Eveille is the most 

 common of the Mississippian forms. Girty states that the shell as 

 figured by L'Eveille is 34.5 mm. wide and 22.5 mm. long, deeply 

 folded, with the two depressions which define the fold so deep as to 

 give the shell a trilobate appearance. The beak is not incurved, so 

 that the round, open foramen is a noticeable characteristic of the 

 typical specimen. (See Monograph XXXII, U. S. Geol. Survey, 

 pt. II, p. 570.) The shell thus described is very different from the 

 one in the Mississippian usually identified as Cleiotliyris roissyi, and 



