NATURAL SCIENCES OF PHILADELPHIA. 415 



also the supero-buccal region ; ventral border very slightly curved. Beaks 

 subterminal, flat, not projecting beyond the dorsal line. Anterior muscular 

 impression circular, deep, behind which is a clavicular process extending from 

 beneath the beaks, at right angles with the dorsal line, half way across the 

 valve. Cast nearly smooth, but marked by a few concentric undulations. 

 Shell very thin, marked simply with fine incremental lines. 



Length -84(100) ; height -39 (46) ; convexity of one valve -11 (13) ; pro- 

 jection of anterior extremity beyond the beak *12 (14). 



Locality. Sec. 29 Moscow, Hillsdale county. 



Sanguinolites Maeshallensis, n. sp. Shell of medium size, transverse, 

 equivalve, ellipsoidal in outline, with subterminal beaks. Hinge line appa- 

 rently edentulous, straight, flattened and elevated posteriorly, terminating one 

 fourth the length of the shell from the posterior extremity, at which point is 

 the greatest height of the shell. Posterior extremity a semi-ellipse ; anterior 

 subtruncate above, regularly rounded below ; a sinus in the ventral border 

 one-third the shell-length from the anterior end, from which a diminishing 

 furrow extends to the flatfish, straight, incurved beak. Greatest thickness 

 of shell on the middle line a little nearest to the anterior end. Surface 

 marked by about three remote, deep, concentric grooves, and numerous fine 

 lines of growth. 



Length 1.2 (100) ; greatest height -(53 (52) ; thickness -36 (30) ; projection 

 of anterior end beyond the beak "09 (7). 



Locality. Marshall. 



This species seems to be destitute of the elongated posterior escutcheon 

 characteristic of McCoy's Sanguinolites, but agrees perfectly with Professor 

 King's modified ideas of Allorisma, (Perm. Foss. pp. 162 and 196). Some hes- 

 itancy is shown, however, among palaeontologists about the adoption of the 

 latter name, which McCoy regards as a synonym of Sanguinolites. 



Sanguinolites boeealis, n. sp. Shell rather small, ventricose, transversely 

 elliptic ; beak somewhat projecting and incurved, less than one fifth the shell- 

 length from the anterior extremity, with a lunuliform excavation in front of 

 it ; dorsal margin straight ; ventral margin slightly arcuate ; posterior ex- 

 tremity regularly rounded ; anterior sharply bent in front of the lunule, from 

 which it slopes with a truncate backward curve to the ventral border ; um- 

 bonal slope extending diagonally to the infero-posterior margin, somewhat 

 angulated behind the beak, and inflected toward the cardinal region. Surface 

 of shell of northern specimens unknown ; cast showing several distinct con- 

 centric grooves. Shell of southern specimens thin, marked both with con- 

 centric and minute radiating stria?. Greatest height of shell along the per- 

 pendicular from the beak ; greatest convexity in the middle of the same line. 



Length 1-10 (100) ; breadth -44 (40) ; thickness of right valve -15 (44). 



Locality. Grindstone quarries, Pt. aux Barques above the gritstones, and 

 Moscow, Hillsdale county. 



Distinguished from S. unioniformis and S. Marshallensis by its terminal beaks, 

 m'eater relative gibbosity, greater length and its posterior attenuation. 



Leptodomus, McCoy. 



Leptodomus clavatus, n. sp. Shell small, tumid, transversely quadrangu- 

 lar, obliquely carinate, concentrically sulcate, with subterminal beaks. 

 Length nearly three times the breadth ; ends abruptly rounded, and slightly 

 deflected upwards, creating a discernible concavity along the extended hinge 

 line. Beak (of left valve) broad, flattened, incurved, with anterior and pos- 

 terior lunettes. Anterior extremity truncate along the anterior umbonal 

 slope ; posterior extremity squarely truncated ; postumbonal slope diagonally 

 precipitous to the cardinal expansion, which begins behind the beak and 

 widens to the posterior extremity. 



Length -62 (100) ; height -24 (39) ; convexity of left valve -10 (16). 



1862.] 



