208 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



second. At the anal side, which is somewhat wider, the first anal plate 

 rests upon the basals, and supports three small plates in the next range, 

 which are succeeded by three plates, and others above. Ventral disk asym- 

 metrical, strongly bulging at the posterior side, and supporting a large 

 central tube. Orals large, excentric. 



Column pentangular ; axial canal small. 



Distribution. — Niagara group of America. 



Eemarhs. — We only recognize Koemer's typical species. Hall's Lamp- 

 terocrinus inflatus {Balanocrinus sculptus Troost MS.) has never been described, 

 and the figure ^ was made from a natural cast, of which the anal side is 

 not seen. Lampterocrinus parvus f w^as also described from very imperfect 

 material. 



Lampterocrinus, by its asymmetry^ and the position of its anal tube, is 

 very closely allied to Siplionocrinus ; but it is readily distinguished by its arm 

 structure. 



Lampterocrinus tennesseensis Eoemer. 



Plate XIIL Figs. 10a, I, c, d. 



I860. Roemer; Silur. Fauna West. Tenn., p. 37, Plate 4, Tigs, la, b. 

 1881. W. and Sp. ; Revision Palfeocr., Part IL, p. 201. 



Syn. Balmiocrinus sculptus Teoost (Catalogue name). 



Calyx elongate, more than once and a half as high as wide, decidedly 

 asymmetrical. Dorsal cup higher than wide, spreading abruptly to the 

 middle of the radials, where it attains almost its full width ; cross-section 

 pentangular. Plates convex, their surface ornamented with conspicuous 

 radiating ridges, passing from the centre of one plate to the centre of an- 

 other — there being one ridge for each side of the plates — dividing the 

 surface into well marked, deeply impressed areas. The ridges are angular, 

 knife-like, their edges more or less serrated ; those from the infrabasals to 

 the basals, and thence to the radials, and between radials and costals, and 

 to the first interbrachials, are more prominent than those of the higher in- 

 terbrachials, but the centre of the latter is raised into a small, sharp node. 



Infrabasals five, completely anchylosed, forming a small cup ; the suture 

 lines obliterated by extraordinary secretion of calcareous matter, and raised 

 into sharp ridges, passing out from the angles of the column to the lower 



* 28tli Rep. N. York State Museum Nat. Hist., Plate 10, Pig. 6. 



t nth Rep. of Geol and Nat. Hist. State of Indiana, Plate 15, Pig. 6. 



