o'AnK.l ENALLASTER TEXANUS. 79 



twice as large as the internal series (PI. xxxix, Fig. 2e). Tlicre are 

 about 35 pairs of pores in tbe petaloidal portion of each poriferous 

 zone. 



The posterolateral pairs are short and quite symmetrical in structure. 

 There are 16 pairs of pores in the petaloidal portions of each i^oriferous 

 zone. 



The anterior unpaired ambulacrum is situated in the anterior grroove, 

 and is wider than the other areas. An elongated pore appears in the 

 external rows on alternate plates. On the intervening jdates the 

 small rows are closely approximated (1*1. xxxix, Fig. 2/). In the lower 

 portion of each column the plates are large and oblong. A pair of minute 

 pores occupy the lower outer corner of each. 



The surface of the test is covered with' a minute granulation, scat- 

 tered among which are numerous small tubercles. 



The apical disk is small and compact, and the four large genital 

 plates are distinctly perforated. The right anterolateral plate occupies 

 the center of the body. The five small oculars are wedged in between 

 the genitals (PI. xxxix, Fig. 2g). 



The mouth opening is transversely oblong and situated in a depres- 

 sion. 



The anal opening is situated high upon the truncated posterior 

 margin, and is small and oval, acuminate below (PI. xxxix. Fig. 2d). 



Belated for 7ns. — It seems not improbable that Spatangus columbiamim, 

 described by Lea in 1840, 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 x)ores 

 in the anterolateral ambulacra, but it is doubtful whether it can be de- 

 pended upon for such details of structure. It seems unwise, however, 

 to replace the term texanus when any doubt upon this point still remains. 



Enallmter peruvianus^ described by Gabb in 1876, from material ob- 

 tained from Peru, seems to be identical. 



Among the European Enallasters none apparently are closely related 

 to Enallastcr texanus. 



Locality and geological horizon. — Enallaster texanus is found widely 

 in Texas in the Fredericksburg forniation of the Comanche series 

 (lower Cretaceous). It is characteristic of the Comanche peak horizon. 



Collections. — U. S. National Museum; Texas Geological Survey j Bos- 

 ton Society of Natural History; Prof. ]vobt. T. Hill. 



Enaxlaster obliquatus Clark. 

 Plate XX,, Figs. la-l. 



Determinative characters. — Test oval, cordiform; upper surface con- 

 vex, flattened and depressed anteriorly, elevated posteriorly; lower 

 surface flat, with j)eristomial depression; apex forward of the center. 

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



