Mabyland Geological Survey 529 



the heavier N&modon. The unusual combination of the Nemodon den- 

 tition, the posterior buttress and the crenate margins seem to justify the 

 description of forms which would otherwise not be noted in the literature. 



The species is quite abundant at the type locality. 



Occurrence. — Monmouth Formation. Fredericktown, Cecil County. 



Collection. — Maryland Geological Survey. 



Genus CUCULLAEA Lamarck 

 [Syst. An. sans Vert, 1801, p. 116] 



Type. — Area concamerata, Martini = Cucullcea auriculifera Lamarck. 



Shell large, heavy, inflated, rhomboidal or cordiform, equivalve or sub- 

 equivalve ; umbones prominent, incurved, separated by a rather wide 

 cardinal area sculptured with divergent ligamentary grooves; external 

 sculpture dominantly radial ; hinge taxodont ; medial teeth transverse or 

 slightly oblique to the hinge margin ; distal teeth sub-parallel to it ; 

 posterior adductor supported by a radial buttress; inner ventral margins 

 crenate. 



Cucullcea is one of the most conspicuous genera in the bivalve faunas of 

 the Mesozoic, particularly toward the close of the epoch. Though much 

 reduced in species it is still abundantly represented by individuals in 

 many of the Eocene faunas. Only three species survive to the present 

 day, all of them denizens of the Indian Ocean or China Sea. 



A. Shell very heavy, altitude of adult exceeding 35 mm.; casts obliquely 



produced posteriorly Cucullcea vulgaris 



B. Shell not very heavy, altitude of adult shell rarely exceeding 35 mm.; 



shell and casts rudely rectangular in outline Cucullcea carolinensis 



C. Shell very heavy, altitude of adult shell exceeding 35 mm.; shell and 



casts conspicuously globose Cucullcea antrosa 



CUCULL.3EA VULGARIS Morton 



Plate XX, Figs. 8, 9 ; Plate XXI, Figs. 1, 2 



Cucullcea vulgaris Morton, 1830, Am. Jour. Sci., 1st ser, vol. xvii, p. 285; 



vol. xviii, pi. iii, fig. 21. 

 Cucullcea vulgaris Morton, 1830, Jour. Acad. Nat. Sci., Phila., 1st ser., vol. 



vi, p. 199. 



Etymology: Cucullus, hood; the outline of the high, incurved umbones is 

 somewhat suggestive of a monk's hood. 



