64 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



surface, and flattened base. In the vicinity of the mouth opening the lower surface is depressed, 

 producing a slight concavity. 



The ambulacra are wide and composed of eighteen to twenty plates. The lower sixteen or 

 seventeen of each series bear prominent tubercles that occur in a continuous line to the peristome. 

 On'either side of the primary tubercles are smaller ones of like shape. The three pore pairs are 

 arranged in semicircular form, the two upper separated from the lower by one of the secondary 

 tubercles. 



The interambulacra are about one and one-half times as wide as the ambulacra and the 

 plates are about fifteen in number. Each plate bears a large tubercle in the center, and irregu- 

 larly arranged about it smaller tubercles of various sizes. 



The peristome is large, with 10 deep incisions. The apical system is lacking, but the discal 

 opening is large and pentagonal in form. 



Related forms. — This unique species is quite unlike any hitherto described, and is readily 

 characterized by the arrangement of the tubercles and pore pairs. As the only representative 

 of the genus in American Cretaceous deposits it has especial interest. 



Locality. — Timber Creek, N. J. 



Geologic horizon. — >Vincentown sand of Eancocas group, Upper Cretaceous. 



Collection. — Academy of Natural Sciences of Philadelphia (1467). 



Genus PEDINOPSIS Cotteau. 



Pedinopsis symmetrica (Cragin). 



Plate XXIII, figures la-h. 



Dumblea symmetrica Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept, p. 150, PI. XXXIV, fig. 12, PI. XXV, figs. 

 4-7; PI. XXVII, fig. 1. 



Determinative characters. — Test medium size, subcorneal, inflated on the aboral surface, con- 

 cave on the adoral surface, sides tumid. Ambulacra with several vertical rows of primary per- 

 forate tubercles, poriferous zones broad, pore pairs biserial. Interambulacra broad and low 

 with many rows of primary tubercles similar to those of the ambulacra. Apical system small, 

 madreporite large, posterior right-hand ocular reaches the periproct. Peristome small. 



Dimensions. — -Diameter 15 to 45 millimeters; height 12 to 33 millimeters. 



Description. — The species referred by Cragin to a new genus which he named Dumblea is 

 evidently a representative of the genus Pedinopsis. A specimen referred to J. W. Gregory of 

 Glasgow was pronounced by him to be a typical Pedinopsis. 



The test is of medium size, tumid, subcorneal, flattened and' concave on the lower surface. 

 The circular ambital outline is somewhat broken by the sutures between the ambulacra and 

 mterambulacra producing an imperfectly defined 15-lobed appearance. 



The ambulacra are rather broad with well-defined poriferous zones. They are covered with 

 two rows of primary tubercles in the smaller and four in the larger specimens. These tubercles 

 are perforate and apparently plain or uncrenulate, although the state of preservation makes it 

 uncertain as to whether delicate crenulation may not have existed. 



The interambulacra are broad and low with many vertical rows of primary tubercles similar 

 to those of the ambulacra. They diminish in number aborally. 



The apical system is small, the madreporite being large and encroaching on the adjacent 

 genitals. The posterior right-hand ocular reaches the periproct. 



The peristome is small with well-marked branchial incisions. The periproct is oval. 



Localities. — Sierra Blanca peaks (type) and near Kent, El Paso County, Tex. 



Geologic horizon.— Washita group of the Comanche series, Cretaceous. 

 Collections. — Geological Survey of Texas; U. S. National Museum. 



