Maryland Geolocucai. Survey 199 



the cardinal extromities truncate or aiwiciuate. Ventral valve the more 

 convex, the greatest convexity being somewhat above the middle; sides 

 regularly curving to the lateral uuirgins, sinus deep and wide towards 

 the front, rounded or flat in the bottom, produced in front, and sharply 

 defined by the adjacent angular plications, which are stronger than the 

 others; beak incurved. Cardinal area elevated and concave. Dorsal 

 valve moderately convex at the sides; the mesial fold abruptly elevated, 

 rapidly expanding below, flattened upon the summit, and usually marked 

 by a mesial depression. Surface marked by from eight to ten or even 

 twelve strong angular plications on each side of the shell, those towards 

 the cardinal extremities being less elevated and often obscure, crossed by 

 concentric zigzag lamellose lines of growth Ijetween which are finer lines. 



A few specimens have been found in Maryland which are referred pro- 

 visionally to this species, the best one of which is an internal impression 

 found on ToAvn Creek, about six miles north of Oldtown. The sinus is 

 deep, about as broad as in specimens of this species, and is sharply de- 

 fined by a plication on each side which is stronger than the others. 

 There are seven prominent plications and two or three inconspicuous 

 ones near the cardinal angle on each side of the shell and tlie con- 

 spicuous i^lications near the anterior margin of the shell are crossed by 

 prominent concentric zigzag lines. The posterior portion of the impres- 

 sion is pustulose, and the hinge-line is rather longer than the greatest 

 width of the shell. The proportions of this specimen are nearer those 

 of Spirifcr sculptilis Hall than of this species and the concentric striae 

 are similar to those on the type specimen of S. sculptilis in the office of 

 the State Paleontologist of New York; but there are only three plications 

 on that specimen while the number of plications for the species does not 

 exceed five on a side according to the description. The Maryland speci- 

 men has nine or ten plications, a character which agrees with S. con- 

 sohriniis and furthermore the sinus is deep and broad as in that species. 



Length, 19 -|- mm.: width, 30 mm. 



Occurrence. — Eomney Formation, Hamilton Member. Town 

 Creek 6 miles north of Oldtown. 



Collection. — Maryland Geological Survey. 



