Maryland Geological Survey 191 



sometimes rounded. Ventral valve most prominent near the umbo, 

 gradually sloping to the cardinal angles; beak incurved; cardinal area 

 moderatel}^ high, vertically striated, and divided by a rather large, 

 triangular delthyrium ; mesial sinus distinct, subangular in upper part 

 and broad deeply rounded depression in front, often with a slight 

 gi'oove along the center and sometimes with a faintly marked plication 

 on each side. Interior of valve shows broad striated muscular impres- 

 sion, the upper part bounded by strong dental plates. Dorsal valve 

 generally the most ventricose with the greatest convexity at about the 

 middle; mesial fold prominent and rounded with medial rounded de- 

 pression. Surface marked by from eighteen to twenty-two simple, low, 

 rounded plications on each side of fold and sinus; entire surface of shell 

 in excellently preserved specimens covered by very fine interrupted longi- 

 tudinal striae which form numerous small pustules or granules, the 

 latter are usually shown on fairly well preserved surfaces; concentric 

 lines of growth and striae are often conspicuous toward the front of the 

 shell. 



The Maryland specimens show the variations of this species as found 

 in New York specimens. It is never as abundant in Maryland as 

 Spirifer imicronatus (Conrad), although a common species at certain 

 localities, as on Evitts Creek below Wolfe Mill. The species is readily 

 distinguished on account of its large size, form, broad plications, and 

 strongly granulose surface. 



Length of average specimen, 48 mm., width, 57 mm.; internal cast 

 length, 38 mm., width, 57 mm. 



Occurrence. — Komney Formation, Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill; in Jennings Eun -J mile west of Cor- 

 riganville; Town Creek Eoad at George Diefenbaugh's ; B. & 0. E. E. 

 cut at 21st Bridge; on Oldtown Eoad east of Maryland Ave., Cumber- 

 land; on the Hancock-Harri.'^onville Eoad about 2 miles north of Han- 

 cock ; McCoys Ferry ; on National Eoad northeast of Cumberland ; along 

 Flintstone Creek in Gilpin ; west of iron bridge over Town Creek north- 

 east of Oldtown ; on National Eoad \ mile west of Licking Creek ; on 

 road east of Pine Hill about 4 miles north of Oldtown; B. & 0. E. E. 



