104 [Assembly 



threadlike striae, which, on the upper side of the volution, are 

 vertical, but turn gently backwards towards the centre, which 

 is marked by a flat revolving band. Length from one to two 

 inches. 



This species resembles the preceding, a variety of which I had for- 

 merly considered it; but the absence of the canaliculation at the 

 summit of the volution, the more depressed convexity and greater 

 attenuation of the volutions, giving a more elongate aperture, are char- 

 acters which appear sufficient for specific distinction. 



Geological formation. Upper Helderberg limestones. 



LOXONEMA PEXATA (n.s.). 



Shell elongate, terete or subfusiform : volutions six or more, 

 gradually expanding from the apex, somewhat flattened towards 

 the upper side, or a little concave just below the suture, and 

 most convex below the middle, last one ventricose ; aperture 

 elliptical. Surface marked by regular elevated transverse 

 striae, which, at the summit of the volution, bend a little back- 

 wards, and again curve forwards above the greatest convexity 

 of the volution. 



Geological formation and localities. In limestone of the Upper Helder- 

 berg group : throughout New- York and in Ohio. This species of Loxo- 

 NEMA, and the two preceding species of Mttrchisonia, are not unfrequently 

 associated together; and as the specimens are usually in the condition 

 of casts of the interior, it becomes very difficult to distinguish the one 

 from the other, more particularly where they have suffered pressure and 

 distortion. 



LOXONEMA BELLATULA ( n. s.). 



Shell moderately elongated, somewhat conical : volutions few, 

 •rapidly expanding from the apex; last volution ventricose, 

 obtusely angular a little below the middle ; aperture trans- 

 verse. Surface of volutions marked by transverse undulating 

 striae, which have their greatest retral curve just above the 



