MARYLAND GEOLOGICAL SURVEY 751 



system moderately elongated. Peristome very near anterior margin. 

 Periproct oval and situated rather high on truncated posterior margin. 



Dimensions. Length 18 mm., width 18 mm., height 11.5 mm. 



Several well preserved casts of this species have been collected. They 

 show some points of similarity to Cardiaster smocH from the Matawan of 

 New Jersey, but the Maryland form is more sharply contracted posteriorly 

 and has a more pronounced anterior surface. 



Occurrence. MOXMOUTH FORMATION. Brightseat, Prince George's 

 County. 



Collection. Maryland Geological Survey. 



Family SPATANGIDAE 



Genus HEMIASTER Desor 



HEMIASTER DELAWAREXSIS n. sp. 



Plate XLVII, Figs. 11-14 



Description. Test small, nearly circular, slightly cordiform, truncated 

 posteriorly ; upper surface slightly convex, elevated posteriorly ; lower sur- 

 face nearly flat; sides inflated; apex nearly central, slightly posterior of 

 the center; ambulacra slightly depressed, posterior pair short, anterior 

 surface broad. Peristome slightly depressed. Periproct small, high above 

 posterior margin. Peripetalous fascicle narrow, distinct. 



Dimensions. Length 22 mm.; width 22 mm.; height 17 mm. 



A single well preserved specimen of this form was collected by Dr. M. W. 

 Twite-hell. It presents some points of similarity to Hemiaster bexeri from 

 the Washita group of Texas, but the height of the present specimen is 

 somewhat greater and the ambulacral furrows are on the whole less 

 depressed. It is also somewhat similar to Hemiaster stella from the Kan- 

 cocas formation of New Jersey, but the latter species has not the broad 

 depressed anterior surface of the present species. 



Occurrence. MATAWAX FORMATIOX. Marl pit south side of Delaware 

 and Chesapeake Canal 1 mile east of St. George's Delaware. 



Collection. Johns Hopkins University. 



