Maryland Geological Survey 357 



nearly parallel; no sinus in either valve [there is a shallow more or less 

 undefined sinus] : dorsal valve extremely elevated, abruptly deflected on 

 each side towards the opposite valve ; beak incurved ; cardinal naargin on 

 each side of the beak profoundly sinuate, for the reception of the promi- 

 nent rounded dental laminae of the opposite valve; anterior and lateral 

 margins uniting by sharp prominent interlocking notches : ventral valve 

 flattened or much the less convex, forming a reg-ular elliptical arch from 

 beak to front, and abruptly deflected upwards at the sides so as to form dis- 

 tinct angles along the lateral margins, the whole front forming a broad 

 truncated projection; beak somewhat obtuse, incurved. Surface marked 

 by strongly elevated, subangular plications, each of which on the front and 

 sides of the shell has a fine depressed line along the center, crossed by fine 

 regular concentric zigzag lines of growth." Hall, 1857. 



As the preservation of this species is not always good and very often 

 the posterior region is absent or the entire shell crushed, C. speciosa 

 appears to be a very vai-iable species. In fact it is very variable in some 

 characters and particularly in the amount of incurvation of the dorsal 

 and more rarely of the ventral anterior margin, in the length (some speci- 

 mens being considerably longer than wide and others as long as wide), 

 and in the presence or absence of a ventral sinus. Usually neither valve 

 has a sinus, but there are specimens with a very broad and shallow one, 

 and occasionally there may even be a small low elevation down the center 

 of the ventral valve. The number of plications varies from twenty-two 

 to thirty-eight. Sometimes the thickness considerably exceeds the width. 



Length about 4.5 cm. ; width about 4 cm. 



C. speciosa appears to be the southern representative of the northern 

 C. barrandii, which is rare in Maryland, and is separated from the latter 

 mainly by its smaller size. 



Occwrrcnce. — ^Oeiskany Formation, Eidgely Member. Knobly 

 Mountain, Miller's Spring, and Williams Eoad near Cumberland, Collier's 

 Run, Maryland ; Pendleton County, West Virginia. 



Collection. — Maryland Geological Survey. 



