1879.] NATURAL SCIENCES OF PHILADELPHIA. 367 



Carabocrinus, in our opinion, is founded upon a malformed or 

 recuperated Gyathocrinus. A comparison of the two genera will 

 show that on the anterior side they are perfectly identical; they 

 also agree most remarkably in the form of the calyx, the construc- 

 tion of the oral side, the delicacy of the arms, and their mode of 

 branching. The only difference is said to be in the construction 

 of the anal area, which, according to Billings, is composed of 

 three plates, the lower one resting upon the underbasals, which is 

 in itself an anomaly such as is found in no other genus. But, 

 further, if Billings's interpretation of the plates in question be 

 correct, the anal area in Garabocrinus would be directed toward 

 the left side of the specimen, which would be the only exception 

 among the Palseocrinoidea, and there exists in no other group of 

 them a basal (subradial of Billings) which is neither radial nor 

 inter radial, and which is disconnected from the radials, as would 

 be the case in this genus. (See Billings's Diagram, Dec. iv. p. 30, 

 and pi. 2, fig. 3 c.) In this specimen, which is the only example 

 in which the anal area has been observed, the small and abnormal 

 so-called subradial and the two anal plates of Billings combined, 

 have almost the form of one of the other basals (subradials) and 

 are but slight^ larger, and we think that in the specimen they 

 originally formed a single plate, which was accidentally broken 

 during the life of the animal and afterwards recuperated, leaving 

 marks of fracture which Billings took to be sutures between the 

 plates. Similar cases are frequently met with among fossil cri- 

 noids, plates being sometimes broken into a dozen or more pieces, 

 which afterwards reunite, each piece retaining the appearance of 

 a true plate. 



Geological position, etc. Billings recognizes the following 



species : 



I 



1856. Carabocrinus radiatus Billings. Type of the genus, and the only species 

 and specimen in which the anal area has been seen. Geo], Surv. Canada, 

 p. 276 j Decade iv. p. 31, pi. 2, fig. 3 a-c. Trenton Limestone, Lower Sil. 

 Ottawa, Canada. 



1859. Carabocr. (?) tuberculatus Billings. Geol. Surv. Can., Dec. iv. p. 33, pi. 10, 

 figs. 2 a-c. Hudson River Gr. Lower Sil. Anticosti. 



1859. Carabocr. van cortlandti Billings. Geol. Surv. Can., Dec. iv. p. 32, pi. 2, 

 fig. 4. Trenton Limestone, Lower Sil. Township of McNab, Canada. 



