Weno and Pawpaw Formations 111 



ENALLASTER 



The genus Enallaster ranges from the Neocomian to the Turonian, but 

 is especially abundant in the subtropical Cenomanian seas, where its great 

 development and exuberance of closely related species constitute a special 

 and complicated problem. The littoral deposits of the Mediterranean and 

 the Texas regions contain a sequence of poorly defined Enallasters, in which 

 the separate species are probably closely restricted in vertical range and on 

 careful study will prove to have great stratigraphic value; the two areas 

 mentioned have closely similar species. 



Enallaster differs from Holaster and Stenonia in having the ambulacra! 

 pores sunk in ambulacral grooves instead of being flush with the surface ; 

 it differs from Hemiaster and Epiaster in the exceptional depth of the 

 anterior unpaired ambulacral groove and in the arrangement and length 

 of the pore zones of the unpaired ambulacrum whose pore pairs are of 

 alternate sizes instead of equal. Enallasters are of very diverse form, 

 one group being flattened and short-ovoid, one group depressed but very 

 elongate, and a third group rather tall and of elliptical contour. 



As defined by Cotteau, Enallaster contains only species in which the 

 anterior unpaired ambulacrum contains alternate long and short pore 

 pairs. Hemiaster differs from Enallaster in having the pore pairs of the 

 unpaired ambulacrum slit-like and similar, and the pores of a pair sepa- 

 rated by a rounded tubercle. The Texas species of Hemiaster are diverse 

 and fall into two general groups. 



A. Postero-laterals very short, biconvex, apical system placed far back 

 on test ; anterior row of antero-laterals with pairs of minute circular pores, 

 form low, with long anterior slope. 



H. longisulcus (Adkins and Winton) 1 . 

 H. riovistae Adkins. 



B. Postero-laterals long, more nearly straight, apical system nearly 

 central ; anterior zone of antero-laterals with larger slit-like pores ; form 

 more elevated and inflated. 



H. calvini Clark. 



H. elegans Shumard^ 



H. whitei Clark. 



H. sp. (Goodland limestone). 



H. comanchei Clark. 



Erroneously referred .to the genus Enallaster. 



