142 LOWER PENINSULA. 



as a subgenus of Zaphrentis, I begin with the description of its 

 species first as being the oldest ones of the type, and let those of 

 Zaphrentis follow them. 



STREPTELASMA CORNICULUM, Hall. 



The original specimens represented and described by Hall, from 

 the Trenton strata of New York, are too imperfect to allow much 

 more than recognition of the general structure. Similar and no 

 better preserved specimens are found in the Trenton strata of 

 Escanaba River, and on St. Joseph's Island and Sulphur Island, 

 situated north of the other. I have represented them on Plate LI., 

 the four left-hand figures in the upper row ; the upper larger 

 specimen is from the lower Trenton strata of Escanaba ; the three 

 lower specimens are from somewhat higher beds on Sulphur Island. 



It is doubtful whether the specimens described under the same 

 name by Milne-Edwards, from the Hudson River group, belong to 

 the same species ; they are found in much better preservation, 

 and can therefore be more specifically described. Elongate conical, 

 symmetrically curved, horn-shaped corals ; middle-sized specimens 

 have a diameter of about three centimeters at the calyx margin by 

 a length of from seven to eight centimeters, but the proportion 

 between length and width of the specimens differs ; some are more 

 elongated, others are shorter than the indicated proportions. The 

 surface of the polyparia is covered by a perfect epithecal crust, 

 with transverse fine wrinkles of growth, and longitudinally striate 

 by septal rugae and intermediate furrows. Milne-Edwards asserts 

 the cells to be covered by an imperfectly developed epithecal crust, 

 but this is an error. Calyces moderately deep, with erect acute 

 margins, steeply inclined side walls, and a variably formed bottom, 

 sometimes narrowed into a blunt end ; at other times broader, 

 rounded, convex in the middle. Lamellae linear, stout, alternately 

 larger and smaller, from 120 to 130 in the circumference of calyces, 

 three centimeters wide. Their surface is decorated by minute 

 granulose rugae, crossing the side faces in an ascending direction 

 from the inside toward the periphery. The radial crests become 

 labyrinthically entangled in the centre of the cells, and usually form 

 a broad convex protuberance. A small septal fovea is always 



