NATURAL SCIENCES OF PHILADELPHIA. 407 



o? 



Length, breadth aD<i thickness of a rather small specimen : '70 (100), 

 (83), and -34 (50). Length of dorsal valve -52 (74.) Length and breadth of 

 another dorsal valve *69 and - 66 



Locality. Light-house, Pt. aux Barques with Rhynchonella Huronensis, &c. 



This species resembles R. serpentina, de Kon. (Anim. Foss., 291, pi. xix. 8), 

 but the ventral valve is most ventricose in the umbonal instead of the middle 

 region, and has a nearly erect instead of a straight beak. It differs from R. 

 vera, Hall (Iowa Rep. 704, pi. xxvii. 3), in the absence of wings, and in its 

 more erect beak. 



Merista, Suess. 



Merista Hooghtoni, n. sp. Shell of medium size, subrotund and subtumid. 

 Ventral valve a little produced at the straight, obtuse foraminated beak ; 

 somewhat truncate in its contour, along the cardinal slopes, and very slightly 

 elongate in front across the width of the sinus ; regularly convex in all di- 

 rections from the middle, except along the shallow sinus, which takes its origin 

 near the middle of the valve. Impressions of the divaricator muscles longi- 

 tudinally striate. Dorsal valve circular; beak scarcely projecting beyond the 

 hinge ; occlusor impressions small, spatulate, separated by a rostral septum 

 reaching one-fourth the length of the valve ; mesial fold represented by an 

 undulation at the anterior margin. Surface of cast smooth. 



Length, breadth and thickness -70 (100), -68 (97) and -36 (51). 



Locality. Light-house, Pt. aux Barques, with Rhynchonella Huronensis, &c. 



Rynchonella, Fischer de Waldheim. 



Rhynchonella Sageriana, n. sp. Shell of medium size, somewhat quad- 

 rantal in outline, rather tumid. Ventral valve not seen. Dorsal valve in the 

 older specimens with a prominent and inflected beak, and about 16 obtuse 

 plications, some of the central ones showing a groove on the summit toward 

 the margin, as if preparatory to bifurcation. Mesial fold consisting of two or 

 three plications just perceptibly raised above the others in the vicinity of the 

 anterior margin. 



Length, -56 (100) ; breadth -60 (107) ; convexity of dorsal valve '23 (41). 



Locality. Marshall, in the Marshall sandstone. 



Rhynchonella Whitei, n. sp. Shell small, sub-circular. Dorsal valve sub- 

 tumid, with the greatest elevation at one-third the distance from beak to an- 

 terior margin ; cardinal slopes slightly convex, terminating in subalate spaces 

 which descend from the umbo ; lateral and anterior margins circularly rounded. 

 Surface marked by about 17 rounded, moderately elevated ribs. Mesial ele- 

 vation entirely wanting, or barely perceptible, and embracing about two of 

 the plications. Median septum present, little developed. 



Length of dorsal valve -38 (100) ; breadth -45 (119) ; convexity -10 (2G). 



Locality. Marshall. 



Rhynchonella Hubbardi, n. sp. Shell small, subquadrantal in outline ; 

 cardinal slopes straight, forming a right angle or more ; lateral extremities 

 about midway of the shell ; anterior border gently curved ; the two valves 

 equally convex ; ventral valve most tumid near the beak, the dorsal in the 

 middle. Surface marked by 21 small rounded radiating plications. Mesial 

 sinus represented by a broad shallow flattening of the mid-frontal slope of the 

 ventral valve, occupying the two middle-fourths of its width, and correspond- 

 ing to 8 or 9 plications. No fold perceptible in the dorsal valve, but a shal- 

 low depression extends from the beak about one-third the length of the shell, 

 corresponding to the extent of the median partition beneath it. Dental plates 

 of the ventral valve well developed, diverging at an angle of about 30. Shell 

 thin, fibrous. 



Length of a ventral valve -26 (100) ; breadth -31 (119) ; convexity, '08 (31). 



1862.1 



