244 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



as the costals ; the two upper shorter and free. There are four arms to each 

 arm opening, the upper bifurcation taking place from the third plate. Arms 

 rather stout and long for the genus ; they are erect, biserial from the last 

 axillary, and have closely set pinnules. Calycine appendages small and short; 

 directed outward, almost at right angles to the calyx. They are composed 

 of single joints, of which the four or ^ye proximal ones of adjoining rays are 

 truncated laterally on apposed sides, and connected with one another by 

 rigid suture ; the plates interlocking. After separating, the two tubes taper 

 rapidly, and terminate at the end of the fourth or fifth joint. The number 

 and arrangement of the interradial plates is quite variable; but in the major- 

 ity of specimens the plate between the radials is succeeded by three plates ; 

 some, however, have but two, except at the anal side which always has 

 three ; there are two or three in the next row, exceptionally four at the anal 

 side. Interdistichals five to six. Ventral disk low-convex, with well defined 

 interradial pits ; the posterior one larger, and containing the anus. Column 

 round ; axial canal sharply stellate. 



Horizon and Locality, — Upper Burlington limestone ; Burlington, Iowa. 



Ti/pe in the Museum of Comparative Zoology, Cambridge. 



Remarks. — Readily distinguished by the upright arms, and short, rapidly 

 tapering tubes. 



Gilbert socrinus reticulatus (Hall). 

 PlaU XVIL Figs, la, K 



1860. Trem,atocrinus reticulatus — Hall; Descr. New Spec. Crin., p. 9; also Boston Journ. Nat. Hist., 



Vol. YII., p. 325. 

 1881. Ollacrinus reticulatiis — W. and Sp. ; Revision Palseocr., Part II., p. 219. 

 1889. Goniasteroidocrinus reticulatus — S. A. Miller; North Amer. Geol. and Palaeont., p. 250, 



Calyx small compared with the preceding species, about as wide as high • 

 dorsal cup urn-shaped with convex sides and a wide and deep concavity 

 at the bottom; ventral disk almost flat. Plates slightly convex, their sur- 

 faces marked by a series of obscure ridges, radiating from the centre of the 

 plates to adjoining ones. The ridges follow the rays, and those passing 

 from the radials to the basals are stronger and somewhat higher ; the latter 

 producing around the basal concavity at the bottom of the calyx the well 

 defined figure of a pentagon with convex sides. 



Infrabasals forming a pentangular disk, of which the angles project quite 

 plainly beyond the column. Basals large, their upper ends curving abruptly 

 upwards, the lower portions of the plates to two thirds their length, together 



