78 



BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Around its superior rim are five arms divided into ten hands. Five elevated 

 ridges ascend from the base and bifurcate before reaching the superior rim, and gives 

 it the angular appearance mentioned above. 



The place for the insertion of the column is small, circular, and perforated by a stel- 

 late alimentary canal. a 



Decatur County, Tennessee. 



Observations. — There are in the Troost collection two species of 

 Periechocrinus. One is Periechocrinus tennesseensis as described by 

 Hall with twenty arms, the other is P. (Saccocrinus) speciosus Roemer 

 (not Hall) which differs from P. tennesseensis in having three arms 

 on each side of the anal area or twenty-two in all. Wachsmuth and 

 Springer say in reference to the latter, "We have in our collection 

 several specimens from that locality with four arms to each ray, but 

 none with three in the posterior rays, as shown in Roemer' s figure, 

 which is said to be a restoration." They discredit Roemer' s figure 

 and unite his species with P. tennesseensis because their collection 

 furnished no specimens showing the three arms on each side of the 

 posterior area, but there are five specimens in the Troost collection 

 that show this feature distinctly. Roemer fully described his speci- 

 men but referred it to P. speciosus Hall from which it differs widely 

 in the number of arms. This specimen differs from those of Troost 

 in having only two arms in the anterior and left antero-lateral ray, 

 but the four arms in the right antero-lateral ray and the tertaxil 

 plate in the posterior half of the left antero-lateral ray indicate that 

 the plan of the specimen is the same as those of the Troost collection, 

 and the differences are probably abnormalities. 



Roemer's species is, therefore, a valid one but requires a new name. 

 I propose for it the name given by Troost to two of his specimens. 

 The name dubius was given to two imperfect specimens which evi- 

 dently belong to the genus Periechocrinus, and they have apparently 

 three arms on each side of the anal area although Troost' s description 

 mentions only two arms to each ray. The specimens are so poorly 

 preserved that their identification is somewhat doubtful, but they 

 seem to belong with Roemer's species. The well preserved specimens 

 of this species were placed by Troost with his Actinocrinites tennesseex, 

 a description of which was published by Hall, as noted above. It 

 appears, therefore, that both species occur at this locality. 



Formation and locality. — Brownsport limestone. Perry and De- 

 catur counties, Tennessee. 



Cat. Nos. 39967, 39982, U.S.N.M. 



a As is mentioned abc "e, my most perfect specimen only exhibited its form and ele- 

 vated ridges, I wa? obliged to take the other characters from a mutilated specimen 

 ij ^hich the arrangement of the plates was visible, nevertheless it is with hesitation 

 thk, I place it in the genus Gilbertsocriniles. — Troost. 



