96 WINCIIELL AND MARCY ON FOSSILS FROM THE 



curved beak, an umbonal slope forming an angle of about 65 with the hinge-line, most ele- 

 vated about midway between the dorsal and ventral margins ; anterior margin parallel with 

 umbonal slope, slightly sinuated below the hinge extremity ; ventral and posterior margins 

 circularly rounded. Cartilage facet narrow, with apparently a single posterior linear 

 groove, deepest near the hinge extremity, and another short, similar groove anterior to the 

 beak. Surface of cast with feeble concentric striae 



Length of hinge-line, .66 inch ; greatest length of shell, .70 inch; height, .78 inch; depth 

 of left valve, 22 inch; length of anterior end, .25 inch; of posterior end .41 inch; projection 

 of beak, .08 inch. 



Differs from Avicula undata Hall, by its shorter hinge-line, more projecting beak, and 

 greater ventricosity. 



Ptcrinea stricecosta McChesney, sp. Ambonychia stricecosta McChesney. "New Paleozoic 

 Fossils," p. 88. This fine species, to the general form of Pterinea, adds a cartilage facet 

 with at least four longitudinal furrows. In one of our specimens the facet is .18 inch wide. 



Pterinea negkcta McChesney. sp. "New Paleozoic Fossils," p. 88. Very abundant in casts, 

 often with the two valves united. Exterior seldom seen. This species possessed a very 

 wide cartilage facet which is rarely seen. 



CLIDOPHORUS Conrad. 



Clidophorus m'chesneyanus W. and M. 



Plate III. figure 3. 



Shell equivalve, with the general aspect of an Orthonota ; but very slightly widening pos- 

 teriorly ; posterior end symmetrically truncate-rounded above and below, so that the most 

 projecting extremity is on the line midway between the dorsal and ventral sides. The dor- 

 sal side is erect, compressed, and the hinge-line is three fourths as long as the shell. The 

 anterior margin is rounded. The beak is very near the anterior end and projects slightly 

 above the hinge. Shell rather ventricose the umbonal ridge lying above the middle and 

 vanishing in the direction of the posterior extremity. The casts prove the existence of 

 deep pyriform pits for the anterior adductors, which are bounded posteriorly by an ele- 

 vated margin scarcely possessing the characters of the "clavicular ridge" of Clidophorus. 

 The posterior scars cannot be detected in any of the specimens. In the left valve was a 

 deep cardinal pit, with a stout cardinal tooth in front of it. The surface of casts is marked 

 by two or three deep furrows of growth, with several smaller incremental lines. Restored 

 exteriors present the same character with increased sharpness. 



Length, 1.11 inch; greatest width three fifths the distance from anterior to posterior 

 extremity .59 inch ; length of anterior end, .15 inch ; thickness of both valves, .4 inch. 



This species differs from Orthonota and Modiohpsis as defined by McCoy, in the possession 

 of cardinal teeth, and from the first, in its deep anterior muscular impression. It differs 

 from Orthonota as restricted by Pictet, in the absence of numerous arcaciform teeth. At 

 the same time it has not the form of Modiolopsis, nor its byssiferous sinus and oblique 

 depression; and we are unacquainted with any established genus with which it strictly 

 agrees. 



We have dedicated the species to Prof. J. H. McChesney, U. S. Consul at Newcastle-on- 

 Tyne, for his investigations made at the typical locality. 



