BATOCRINIDiE. 521 



sible they may have to be separated subgenerically, perhaps under 

 Pradocnnus. 



The anus of Penechocrinus is rarely observed, and throws no light on the 

 relations of the genus. P. moniliformis was probably provided with a short 

 anal tube, while most of the other species seem to have had a mere 

 protuberance. 



Pradocnnus de Verneuil (1850) is possibly identical with Periecliocnmts, 

 and also Geocrinus d'Orbigny, which was proposed in the same year. Johannes 

 Mliller referred Pradocnnus to Pt/xldocrinus, under which he proposed to em- 

 brace all Actinocrinidse possessing interdistichals. Angelin identified Troclio- 

 crinites Pander with Perieckocrinus ; while Bigsby took it to be a synonym of 

 Gl//pfocrinus. The name Trochocrinites was preoccupied by Portlock in 1848, 

 but T. Icevis, the only species referred to it, was described from an imperfect 

 specimen, and its relations cannot be accurately determined. Hall's Actino- 

 crinns semiradiatus, which is known only from natural casts, and which we 

 formerly referred to Periechocrimis, is possibly a Macrostylocrimis. S. A. Mil- 

 ler's Saccocrinus Gorhyi, from Decatur Co., Ind., is described from a cast, and 

 it is douhtf ul if it belongs to this genus. 



Periechocriims speciosus (Hall). 

 Plate L. Figs. 6a, b. 



1862. Saccocrinus speciosus — Hall; Palseont. N. York, Vol. II., p. 205, Plate i6. Figs. 1, 2. 

 1881. Periecliocriims speciosus — W. and Sp. ; Revision Palaiocr., Part II., p. 133. 



Rather large. Calyx elongate ; sides but little convex ; greatest width 

 across the first distichals ; plates smooth, even without the usual radial 

 ridges. 



Basal cup very deep. Eadials and costals once and a half as long as wide, 

 decreasing in size in ascending order, their upper and lower faces exceed- 

 ingly narrow, the upper sloping faces of the radials unusually short. Dis- 

 tichals four ; the first about half the size of the first costals ; the second 

 much smaller ; the upper ones, which are followed by free arm plates, short 

 and quadrangular. Arras branching a little above the calyx, and twice again 

 higher up ; they are proportionally thin and taper gradually to the tips. 

 Interbrachials rather large ; the first followed by five or six ranges of two 

 plates each. Interdistichals in three or four rows. Construction of the anal 

 side not known, nor the structure of the tegmen. Column round ; the nodal 

 joints slightly projecting ; their edges covered with a row of small nodes. 



