CARBONIFEROUS AQB. PE 11 M I A X PERIOD. 57 



Bnkevellia parva. 



(1>LAT II, Kig. 12, a, A.) 



BaJcnellia parva, MEEK & UATDIX, Tram. Albany Inst. IV, March 2.1, 1858. 



Shell very small, obliquely subovate, oblong, or subrhombic in outline ; valves gibbons along the oblique nmbonal 

 slope*. Antero-ventral margin sloping very obliquely backwards and downwards ; rather distinctly sinuous uinli-r 

 tin- l.i-.ikM. I'oatero- banal extremity roauded ; anal edge sinuous above; anterior extremity somewhat lobed, sub- 

 angular or very narrowly rounded. Hinge line straight, nearly or quite equalling the greatest length of the shell, and 

 ranging at an angle of about :>."i to tlio nmbonal prominences. Beaks rather small, rising a little above the hinge, 

 incurred, and located about half way between the middle and the anterior extremity. Postero-dorsal region com- 

 preesed, or more or lens alatv, and terminating at a distinct angle at the extremity of the hinge. Surface with 

 concentric striae. Anterior teeth of hinge, one or two to each valve, linear and declining a little in front ; posterior 

 ti-i-tli. one or two, long, linear and ranging parallel to the hinge margin. 



Length, 0.20 Inch ; height, (Me in, -h ; thickness or convexity of the valve*, about 0.08 inch. 



We can scarcely regard it as a clearly established fact that this little shell 

 prNMMM ;ill tin- characters of Prof. King's genus Buki nll'ia, since its cardinal area 

 and muscular and pallia! impressions have not yet been seen. It agrees, however, 

 MI exactly in form and general appearance, as well as in the nature and arrange- 

 ment of its hinge teeth with that genus, and differs so materially in the latter 

 character and the absence of a l>\-vil sinus from Pteria, that we do not feel war- 

 ranted in removing it from the genus in which we first provisionally placed it. 



It agrees very nearly in form with some varieties of Bakevellia antiqua, Munster 

 (sj>.), but is uniformly much smaller never being more than one-fourth the average 

 si/e of that shell; while its cardinal area must be much narrower, judging from 

 the close proximity of the beaks ; the posterior extremity of its hinge is also much 

 more angular. 



Locality and position. Near the mouth of Smoky Hill fork of Kansas River; 

 on Cotton-Wood Creek, and at numerous other localities in northeastern Kansas ; 

 in beds of yellowish magnesian limestone of Permian Age. (Type 3959.) 



FAMILY TRIGOXIID^E. 



Shell equivalvo, generally inequilateral, closed, varying greatly in 

 form and ornamentation, according to the several genera and smaller 

 groups, nacreous within. Ligament external ; hinge composed of a few 

 diverging, usually large, interlocking teeth. 



Animal with two recumbent gills on each side ; palpi simple ; mantle 

 open ; foot long, lanceolate, bent, and formed for leaping. 



This family includes the following genera: Schizodus, Myophoria, Trigonia, and 



V, rti<-< n-il in ? The first two of these genera are entirely extinct, while the Trigonias, 



which were most abundant during the Jurassic and Cretaceous epochs, are still 



represented by a few living species. Of the genus Verticorrfia, only one or two 



Tertiary species, and one living species are known. 



In tracing the different groups of this family, from its first appearance in the 

 Palaeozoic rocks, as plain shells (Schizodus) with smooth weak hinge teeth, it is 



8 liar. 1864. 



