CRETACEOUS ECHINODERMATA. 87 



The apical system is small and compact, and the four large genital plates are distinctly per- 

 forated. The right anterolateral plate occupies the center of the disk. The five small oculars 

 are wedged in between the genitals. 



The peristome is transversely oblong and situated in a depression. 



The periproct is situated high upon the truncated posterior margin and is small and oval, 

 acuminate below. 



Related forms. — It seems not improbable that Spatangus columbianum, described by Lea 

 in 1S40, from the United States of Colombia, may prove to be identical, or at least very closely 

 related to the Texan form. The indistinct figure shows a different arrangement of the pores 

 in the anterolateral ambulacra, but it is doubtful whether it can be depended upon for such 

 details of structure. 



Enallaster peruvianus, described by Gabb in 1876, from material obtained from Peru, seems 

 to be identical. 



Among the European Enallasters none apparently are closely related to Enallaster texanus. 



Localities. — Very common near Fredericksburg (type), Leon Springs (figured specimen), and 

 at numerous other localities in Texas, and near Inichtea, N. Mex. 



Geologic horizon. — Trinity, Fredericksburg, and Washita groups of the Comanche series, 

 Cretaceous. 



Collection. — U. S. National Museum (9857). 



Enallaster obliquatus Clark. 



Plate XL, figures la-1. 



.Enallaster obliquatus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 

 Enallaster obliquatus Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 79, 80, PL XL, figs. la-1. 



Determinative characters. — Test oval, cordiform; upper surface convex, flattened and 

 depressed anteriorly, elevated posteriorly; lower surface flat, with peristomial depression; apex 

 forward of the center. Ambulacra narrow, unequal. Surface of the plates covered with small 

 tubercles and intervening microscopic granulation. Apical system compact. Peristome trans- 

 versely subpentagonal. Periproct situated on truncated posterior margin. 



Dimensions. — Length 49 millimeters; width 45 millimeters; height 26.5 millimeters. 



Description. — This species has a broad cordiform test, flattened and slanting on the anterior 

 upper surface, whence the name obliquatus. The anterior groove is deep, wider at its head, and 

 cuts broadly into the anterior margin. The posterior portion of the test is elevated near the 

 apex and obliquely truncated toward the margin. The sides are sloping anteriorly, fuller pos- 

 teriorly. The base is flat with a deep peristomial depression. 



The ambulacra are narrow and unequal. The anterolateral pair are slightly depressed 

 and curved backward in the upper portion. The pores are unequal, those of the anterior zone 

 small and near together, those of the posterior elongated, the outer much more so than the inner 

 series. There are about 40 pairs of pores in each zone. 



The posterolateral pair- are short and slightly depressed. The pores are more nearly equal 

 and about 24 pairs are found in each zone. The single ambulacrum is placed in the anterior 

 groove and is much wider than the paired ambulacra. The pores of the different plates vary in 

 size and position. The plates in the lower portions of the areas are large and oblong hi form. 



The surface of the test is covered with minute tubercles between which is a microscopic 

 granulation. The apical system is small and compact. 



The peristome is transversely subpentagonal. The periproct is oval and situated high on 

 the truncated posterior margin. 



Belated forms. — E. obliquatus is separated from E. texanus, the only other representative 

 of this genus from the Cretaceous deposits of the United States, by its broader depressed form, 

 more sunken anterior sulcus, and lower position of the periproct. These features seem to be 

 characteristic of nearly all the forms from the Glen Kose beds and perhaps should not be re- 

 garded as of specific value. Some specimens more or less intermediate in their characters are 



