DOTTLINO. 
SILURIAN FOSSILS 
47 P 
MylUarca pernoid^s, sp. nov. 
Shell compresKOtl convex, rather obliquely subovate and very inequi- 
lateral, or broadly inytiloid and aubalate behind. Anterior side very 
short, truncated or abruptly inflected above and rounded l^elow ; pos- 
terior side a little longer, its outer margin truncatefl somewhat obli- 
quely and forming an angular or subangular junction with the cardinal 
border above, but rounded below Cardinal border behind the beaks 
straight, its entire length equal to fully two thirds or more of the 
greatest length of the valves below ; hinge area large ; umbones appa- 
rently not very prominent ; beaks appressed, incurved and almost 
terminal. 
Surface marked with a few impressed and concentric stria* of growth ; 
test rather thick. 
Hinge with both cardinal and lateral teeth; muscular impressions 
unknown. 
Ekwan river, portage road at falls : one testiferous left valve. 
jMr. Ulrich thinks that this shell is “closely related to, if not quite 
the same as, AmhonycJiia apJitm, Hall," from the Niagara limestone of 
Illinois, which he (Mr. Ulrich) referred to Mytilarmm 1804, in the 
seventh volume of the Reports of the Geological .Survey of Ohio. A. 
aplum, however, was based upon a mere east, which doe.s not .show the 
proportionate length of the hinge line, the size of the cardinal area, 
nor the surface markings, .so that it is scarcely liossible to make a satis- 
factory comparison between it and the specimen from the Ekwan river. 
Ctenodonta tnibm'ala, sp. nov. 
Shell small, inequilateral, moderately convex, subovate and one 
fourth longer than high. Anterior (?) aide .short .and rounded : poste- 
rior (?) side produced, a little longer, and more narrowly rounded at its 
outer termination ; ventnil margin gently convex : superior border 
sloping abruptly downw,ard in front of the beaks ami much more grad- 
ually .so behind them; umbones small and modei-ately prominent; 
beaks also small, incurved and placed in advance of the midlength; 
ligament external, short, placed on tbe shorter end of the hinge line. 
.Sui-face faintly, very minutely and concentricallv striated. 
Hinge dentition and muscular irnprc.ssions unknown. 
Dimensions of the only specimen collected : maximum length, twenty 
millimetres ; gi*eatest height, fifteen mm. and a quarter ; maximum 
thickne.ss, ten mm. and a (piarter. 
