544 GEOLOGY OF OHIO. 



siphuncle is almost invariably well shown; it is only moderately excen- 

 tric. Most of the casts are perfectly regular and present nothing un- 

 usual. In others, however, the surface of the cast shows on one side a 

 vertical series of markings which are so regular in size and form as to 

 indicate that they are connected with some internal structure of the shell. 

 These markings consist of an impressed line which rises from each lower 

 septum to about half the height of the chamber, and then falls again, 

 describing a convex curve extending from one-fourth to one-third the 

 distance around the shell. Apparently the region along this line often 

 weathers away and in that case the part below the impressed line remains 

 behind as a triangular projection with rather concave lateral sides, bounded 

 along these sides by deep grooves which gradually disappear laterally 

 along the lower septum, but which unite above and reach the upper 

 septum. The bottom of these grooves is at times pitted, and the exterior 

 of the casts also at times shows very faint vertical lines, which may be 

 pitted, but at present it is no longer possible to place, any stress upon 

 this pitting since it is too exceptional, and seems to be simply a sign of 

 weathering. Although the termination of the septa at the siphuncle is 

 well shown in longitudinal sections, the siphuncle itself is almost never 

 seen, and even then not satisfactorily. The best section indicates that 

 it was cylindrical, and narrow, a view which gains support from other 

 specimens described next. 



In the "Orthoceras block" at Huffman's Quarry were found in con- 

 siderable numbers a species of Orthoceras which in its rate of tapering, 

 slightly excentric siphuncle and curvature of the septa resembles the 

 marl specimens from the same quarry. The septa seem in general to be 

 rather more closely arranged. The siphuncle is cylindrical. The 

 exterior surface of the shell is marked by transverse rings or striae, 

 which are very variable in distinctness but which in general may be said 

 to gain in strength and distinctness and to grow more distant in the 

 larger, later parts of the shell. Quite a typical rate of curvature is shown 

 \sy a specimen 20.5 mm. long, with diameters of 2.9 mm. and 5.3 mm. at 

 the. opposite ends. In another specimen 30 mm. long, the diameter 

 increases from 3.8 mm. to 8.2 mm. Now this larger diameter approaches 

 closely to the smaller diameter of a larger specimen also with transverse 

 but coarser striae and a cylindrical siphuncle, at times showing a 

 slight tendency toward annular structure. This specimen in a length of 

 19.5 mm. increases in diameter from 8.7 mm. to 11.2 mm. and shows 12 

 septa; the siphuncle is 1.4 mm. wide at the larger end, a rather abnormal 

 width for this size. Another specimen with a siphuncle 1.2 mm. wide 

 reaches a width of 13.3 mm. at its larger end. The larger specimen col- 

 lected had a diameter of 17 mm. There seems no reason for separating 

 the larger specimens from the smaller ones described earlier, and there- 

 fore small size ceases to be a distinguishing feature of this species, 

 although most specimens found are small. At a point 3.7 mm. in dia- 



