Maryland Geological Survey 531 



region, where it lends a somewhat punctate aspect to the shell by cutting 

 up the grooves between the incrementals into a series of minute pits; con- 

 centric sculpture incremental in character but over-riding the radial, 

 resting stages crowded and conspicuous toward the ventral margin ; 

 cardinal area high rhornboidal, suleated with concentric diamond-shaped 

 ligament grooves which vary in number with the age of the individual 

 but may be as many as nine in the adult ; hinge line straight, from a little 

 less than one-half to more than two-thirds the total latitude ; ventral 

 margin of the hinge plate gently arcuate, dentition vigorous, the medial 

 teeth discrete, the distal teeth hook-shaped, the number of vertical teeth 

 larger both absolutely and relatively in the adult form; muscle scars 

 very prominent, the anterior high up under the hinge plate, the posterior 

 buttressed by a prominent radial groove; pallial line simple, rather near 

 the base ; inner margins not crenulated. 



The casts of C. vulgaris Morton, the form in which the species most 

 commonly occurs along the middle Atlantic slope, are conspicuous for the 

 high, compressed umbones and the obliquely produced posterior keel. The 

 groove is very deep but is not greatly produced dorsally. The great thick- 

 ness of Cucullcea shell, particularly in the medial portion, leaves a rela- 

 tively small cavity, thus giving a surprisingly compressed cast. 



C. capax, described by Conrad from the Eipley of Mississippi, is prob- 

 ably identical with C. vulgaris, though it may be consistently more inflated. 

 The fact that the northern form is represented most frequently by casts 

 and the southern by the original shell makes it difficult to determine their 

 exact relationship. 



Occurrence. — Matawan Formation. Camp Fox, Chesapeake and 

 Delaware Canal ; Post 198, Chesapeake and Delaware Canal ; Camp IT & I, 

 Chesapeake and Delaware Canal: Post 157, Chesapeake and Delaware 

 Canal, Delaware; north shore Pound Bay, Severn River, Anne Arundel 

 County, Maryland. Monmouth Formation. John Higgins farm, 2 

 miles west of Delaware City, Bohemia Mills, Cayots Corner, right bank of 

 Bohemia Creek near Scotchman's Creek, Cecil County ; Brightseat, Brooks 

 estate near Seat Pleasant, Fort Washington, Prince George's County. 



