304 PROCEEDINGS OF THE ACADEMY OP [1881. 



possess a simple anal opening, others with apparently a small 

 ventral tube, but we were obliged to do so, because the construc- 

 tion of the ventral disk is so little known, that a subgeneric 

 division in this case could not as yet be carried out practically. 



Pradocrinus de Yerneuil, 1850, is identical with Austin's genus, 

 also Geocrinus d'Orbigny, which was proposed the same year, 

 and based upon Miller's Actinocr. moniliformis. Job. Miiller 

 referred Pradocrinus to his Pyxidocrinus, a genus in which he 

 proposed to embrace those species of the Actinocrinus group 

 which possess interaxillary plates. Angelin identifies Trocho- 

 crinus Pander with Periechocrinus, while Bigsby takes it to be 

 a synonym of Glyptocrinus. Trochocrinites Gothlandicus, 

 certainly differs in several respects from typical species of 

 Periechocrinus. 



The name Trochocrinites was preoccupied by Portlock in 1848. 

 His only species P. Isevis was described from a very imperfect 

 specimen, and we cannot accurately determine its relations, though 

 it seems to be allied to the group of P. Gothlandicus. It is cer- 

 tainly quite distinct from Angelin 's P. Isevis. We should be 

 inclined to place this species with P. Gothlandicus, P. radialus, 

 and P. pulcher in a separate group under Portlock's name, but it 

 is possible they all belong to Glyptocrinvs, and we dislike to 

 encumber the subject with generic separations based upon such 

 imperfect data. 



Austin made Periechocrinus the type of a distinct family, and 

 included in it Sagenocrinus, while Pictet and Zittel refer it to the 

 Actinocrinidfe. 



Generic Diagnosis. — Body large, elongate and somewhat urn- 

 shaped ; composed of thin, almost smooth or delicately sculptured 

 plates ; radials marked along their centres with a conspicuous 

 elevated ridge, passing from plate to plate, which divides upon 

 each axillary piece, and which toward the arm-bases increases in 

 prominence, until it gradually becomes identified with the free 

 arms. Symmetry bilateral. 



Basals three, of equal size, united into a spreading cup ; 

 articulating facets for the reception of the column wide. 



Primary radials 3X5, comparatively long and narrow, con- 

 necting line unusually short, sometimes joining only by the point 

 of an angle. The first radials large, alternately hexagonal or 

 heptagonal ; the second hexagonal and smaller ; the third smaller 



