Genus Murchisonia, D'Arcliiac 



MuRCHISOJsIA ? PROHXA (n. Sp.) 



Shell extremely elongate, spire much elevated, turritiform or subu- 

 late. Whorls eight or ten, very gradually increasing in size from the 

 apex, flattened or slightly convex on the outer surface, with a very 

 moderate angularity in the middle ; the last one equal in length to 

 the two preceding ones, somewhat angular at the lower lateral bor- 

 der, depressed convex below ; suture distinct, not channeled. Aper- 

 ture broadly subovate, sharply angular at the upper side, and rounded 

 below ; columella slender, arcuate or sub-spiral. 



Surface marked by strong revolving lines on the surface of the 

 volutions, the central one strongest and most prominent ; finer revolv- 

 ing lines mark the under side. 



The extremely attenuated spire, and the flattened volutions, are 

 characters by which it may easily be recognized. The strong re- 

 volving lines give it much the appearance of a Turritella, and as the 

 surface of our shells has been exfoliated, it is with some doubt we 

 place it under Murchisonia. 



Genus Porcellia, Leveille. 



PORCELLIA CRASSINODA (n. Sp.) 



Shell large, discoidal, consisting of three to four volutions, which 

 rapidly increase in size from the apex ; contiguous or very slightly 

 embracing. Volutions sub-triangular, rapidly increasing in diameter 

 from the venter to the dorsum, the relative diameters of which are 

 as two to five, exclusive of the nodes on the dorso-lateral angles ; the 

 diameter from the ventral to the dorsal margins being a little greater 

 than the breadth of the back. Lateral surfaces slightly convex ; back 

 gently rounded, marked along the middle by a shallow groove marking 

 the position of the slit in the aperture. Dorso-lateral angles orna- 

 mented by a single row of distant, strong, obtusely-pointed nodes, 

 those of one side a little in advance of those on the other. 



Surface marked by fine, flexuose, revolving strise on the back, and 

 by revolving and transverse striae on both sides and back. Margin of 

 the aperture broadly sinuate on the dorsum, with a narrow notch in 

 the middle. 



This shell differs conspicuously from P. nodosa, Hall (Geol. Survey 

 of Iowa, Sup. to Vol. I., Part ii., page 92), in the subtriangular form of 

 the volutions, and in the stronger nodes of the dorso-lateral angles, ag 

 well as the less numerous and more rapidly increasing volutions. 



