74 MESOZOIC ECHINODERMATA OF THE UNITED STATES. [bull. 97. 



HOIjASTERID^E. 



Test ovate or cordate. Ambulacra narrow ; poriferous zones narrow, 

 pores unigeuiiual. Apical disk elongated, at times so mucli that the 

 three anterior ambulacra are widely separated from the two posterior. 

 Mouth opening exceutiic, anteriorly situated. Anal opening infra- 

 marginal or marginal. 



ANANCHYTES Mercati. 



Ananchytes ovALis Clark. 



Plate XXXVI, Fig. 1 a-h. 



Determinative characters. — Test subovate cordate; contracted i)os- 

 teriorly; upper surface convex; lower surface flat. Apical disk elon- 

 gated, consisting of four perforated genital and five ocular plates 

 situated slightly forward of the center. Mouth opening near the an- 

 terior margin. Anal opening oval, situated on a slight protuberance 

 of the posterior margin. 



Dimensions. — Length, If inches; width, li inches; height, flinches. 



Description. — The two s])ecimeus of this si)ecies collected by the 

 writer are remarkably well lireserved and admit of the determination 

 of all the essential features. The test is in lateral outline subovate, 

 though somewhat cordate in form when viewed from above or below. 

 A marked protuberance (PI. xxxvi, Fig. le) is present on the posterior 

 margin that appears as a slight ridge on the lower surface between 

 the mouth and anal openings. The upper surface is convex. The sides 

 are full and rounded at the ambitus. The base is nearly flat, with the 

 exception of the slight ridge and depressed mouth edges. 



The ambulacra! areas are wide aiul straight, attaining their greatest 

 width just above the ambitus. The pores are oval, and those of each 

 pair are placed at an angle to one another (PI. xxxvi. Fig. Ig). The 

 surface of both the anil)ulacral and interambulacral plates is covered 

 by small tubercles, between which are numerous microscopic granules. 

 The apical disk is elongated (PI. xxxvi. Fig. 1/). The four genital 

 plates are large and distinctly perforated. The anterior, right-hand 

 genital plate, which serves as the madreporite, is nuich larger than any 

 of the others, being several times the size of the anterior left-hand 

 genital, with which it is iu contact. The posterior genitals are very 

 nearly of ecpial size. 



The mouth opening is transversely oblong and situated near the an- 

 terior margin. The anal opening is oval and situated on a marked 

 protuberance on the posterior margin. 



Related forms. — The present species is the only rex)resentative of the 

 genus recognized from American deposits. It is more ovate and less 

 elevated than the forms described from European strata. 



