170 PROCEEDINGS OF THE ACADEMY OP 



net of Nat. Hist., though not with Mr. Salter's figures of P. Miltoni. It will 

 probably be found to be genericallj distinct frona the iSilurian typical forms of 

 Protasfcr, but we prefer to place it provisionally in that genus for the present. 

 We are not aware that an}' well defined species of the genus Frotaster, how- 

 ever, have been found in Carboniferous rocks. 



Locality and position. Crawfordsville, Indiana. Keokuk division of the 

 Lower Carboniferous series. 



MOLLUSCA. 

 Genus CH^NOCARDIA, M. and W. 



(;^^5t(Va), to gape ; K^fiia, the heart; in allusion to its gaping front and gene- 

 ral form). 



Shell equivalve ? rather thin, verj' inequilateral, more or less oval, beaks 

 small, depressed and nearly terminal ; valves strongly gaping in front, and 

 closed behind ; hinge unknown, but short and without cardinal area ; surface 

 with concentric strias, crossed on the posterior dorsal region by faintly marked 

 radiating costte, and on the gaping front bj' radiating lines and costas. 



Although we have not seen the hinge of this type and know very little of its 

 muscular* and pallial impressions, it differs so decidedly in its external 

 characters from all the established genera known to us, that we cannot doubt 

 the propriety of proposing a new genus for its reception. In the single char- 

 acter of having the valves distinctly gaping anteriorly, it resembles the Silu- 

 rian genus Hippomya of Salter, to which it may bear some relations. It 

 diflfers, however, in having the gaping part of the valves terminal, instead of 

 occupying the anterior ventral region, w hen placed with the hinge line in a 

 horizontal position, the margins of the gaping part (which are not thickened 

 and reflected as in Mr. Salter's genus), are found to slope slightly forward, as 

 if truncated, in that direction from immediately in front of the beaks, instead of 

 sloping posteriorly to the middle of the basal margin. Uur type also differs in 

 the possession of radiating markings, and much smaller umbones, as well as 

 in being less gibbous. It is true that some of these characters might be 

 merely specific, but we cannot believe they all are ; while the general physiog- 

 nomy of the two forms is so different as strongly to impress the mind with the 

 ■idea of their belonging to entirely distinct genera. 



Without a knowledge of its hinge and interior, it is not possible to arrive 

 at very satisfactory conclusions in regai'd to the family relations of this shell, 

 though we are inclined to believe it related to the Mi/tihdx. The gajjc of the 

 front was doubtless for the passage of a byssus, as it is too high up from the 

 antero^ventral margin to have been for the protrusion of a fool to be used in 

 ^crawling about. 



The description is made out from left valves only. 



Ch^nocardia ovata, M. and W. 



Shell obliquely ovate, more than two-thirds as wide as long, moderately 

 gibbous, the greatest convexity being a little in front of the middle. Posterior 

 outline rounding into the cardinal margin above, and into the base with a 

 broad subsemicircnlar curve ; deepest part of the base behind the middle, from 

 near which the anterior ventral margin ascends verj' abruptly and a little 

 otjliquely forward, with a slightly convex outline, to the lower part of the 

 anterior hiatus. Anterior gaping edge truncated, with a slightly convex out- 

 line and forward slope from immediately in front of the beaks, and defined, or 

 separated from the body of the shell by a faint sulcus, starting from the imme- 

 diate front of the beak, and curving downward so as to intersect the margin 

 at the base of the hiatus, which (supposing it to be equally developed in the 



* One internal cast appears to show trace of a long narrow, anterior adductor muscu- 

 lar scar near the edge of the gaping part of the valve. 



[July, 



