NATURAL SCIENCES OF PHILADELPHIA. 
263 
AlLORISMA ? ALTIROSTRATA, D. Sp. 
Shell oblong oval, very gibbous in the umbonal region ; beaks much elevated 
above the cardinal edge, incurved, and located over the anterior end. Posterior 
extremity more compressed, but apparently more or less gaping, rounded in out- 
line, anterior end vertically subtruncate, somewhat gaping ; base nearly straight, 
or a little concave near the middle, rounding up towards the extremities. Car- 
dinal border rather short, straight and inflected so as to form a moderately dis- 
tinct, impressed area for the reception of the ligament. Surface of cast marked 
by concentric undulations, which are narrower, more regular, and distinct on 
the umbones and over their slopes, than towards the base and extremities. 
From the anterior side of the beaks, there is on each valve, an obscure sulcus 
descendiug obliquely and widening towards the middle of thebase. Length 3-06 
inch ; height from the base to dorsal margin 1-63 inch ; do. to highest part of 
beaks 1"74 inch ; greatest transverse diameter. 
Having ooly seen an internal cast of this shell, showing neither the muscular 
norpallial impressions, and giving no clue to the character of the hinge, there 
must remain some uncertainty respecting its generic relauons. Its most marked 
peculiarity is the unusual elevation of the beaks, which gives it much the form 
of some of the Jurassic Pholadomyas. We know of no other shell from the whole 
Carboniferous System with which it can be confounded. 
Locality and position. — Grasshopper Creek, K. T., Upper Coal Measures. 
Allorisma subcuneata, n. sp. 
Shell large, clavate, cuneate, gibbous in the anterior and umbonal regions, 
contracted and compressed posteriorly. Beaks depressed, incurved and re- 
moved about one eighth the length of the shell from its apterior extremity. Pos- 
terior end narrowly rounded, and apparently gaping a little; buccal end olb- 
liquely truncate above, rather narrowly rounded, and somewhat gaping below. 
Base nearly straight along the middle, curving up very gradually behind, and 
abruptly in front ; dorsal outline sloping slightly from the beaks towards the 
anal extremity. Surface of cast marked by more or less regular concentric un- 
dulations; hinge long and straight; lunule oval, not very well defined ; ligament 
area long and narrow, bounded on either side by a narrow obscure ridge, on the 
outside of which there is a long, parallel, shallow undefined sulcus. Anterior 
muscular impression lunate, the upper extremity curved back over itself so as to 
give the whole somewhat the form of the letter G ; posterior muscular impres- 
sion, large, oval, ovate, or rhomboidal, located about one third the length of the 
shell from the posterior end ; pallial impression faint, having a deep angular si- 
nus. Length 5-10 inch ; height 2-25 inch ; greatest thickness near the anterior 
end 1-70 inch. 
This species is very similar to Sanguinolites clava of MeCoy, but its ventral 
margin is straighter, its beaks rather more depressed, and its anterior border 
more narrowly rounded below the beaks. The lunette on the anterior side of 
the beaks, in our shell, appears to be less distinctly defined than is represented 
in Prof. McCoy's figure, while the anterior muscular impression m S. clava ap- 
pears to be orbicular instead of lunate as in our shell. 
Locality and position. — Leavenworth City, in upper coal measures, 
Allorisma? Leavenworthensis, n. sp. 
Shell very thin, oblong, subcylindrical behind, more compressed anteriorly; 
posterior end broad, rather obliquely truncate, very widely gaping, or even di- 
lated at the margins ; buccal end narrowly rounded and nearly closed. Base 
almost straight, or but slightly convex, rounding up gradually in front and much 
more abruptly unto the truncate posterior border. Dorsal outline concave from 
the beaks to its elevated posterior extremity. Beaks moderately elevated, slight- 
ly flattened," more or less angular behind, incurved, and located about half way 
between the middle and the anterior end. Surface marked by obscure concen- 
1858.] 
