534 GEOLOGY OF OHIO. 



practically without value excepting as a means of calling the attention of 

 collectors to the possibility of finding this form at the locality named. 



Cyrioeeras Cihitonense, sp. nov. 



(Plate 36, Pig^s. 2 a, b, c, d, e.) 



In the upper shaly courses at Huffman's Quarry was found a speci- 

 men measuring 55 mm. along its convexly curved side which describes 

 an arc of 67°, and 29 mm. on its inner or concave side which describes 

 an arc of 40°. Laterally the shell is strongly compressed. The inner 

 concave side remains distinctly and quite evenly rounded, while the outer. 

 or convex side is angulated by the meeting, along this side, of the two 

 lateral flattened faces of the shell at almost a right angle. The specimen 

 shows 14 septa, the later formed ones becoming rapidly more distant and 

 larger, and describing an angle of 40°. The transverse diameters at the 

 smaller end are 12 mm. and 7 mm., at the larger end 30 mm. and about 22 

 mm. The siphuncle is contracted as it passes through the septa, and the 

 separate divisions meet each other obliquely, but in longitudinal sections 

 the divisions of the siphuncle present a nearly tubular outline, though en- 

 larging somewhat above, if the contraction immediately at the septa be not 

 considered. The siphuncle lies within 2 mm. of the outer margin. The 

 width of the siphuncle at the larger extremity is 6 mm. Careful exami- 

 nation of the curvature of the septa showed that in general these were 

 regularly concave, but that towards the outer and inner sides, for a short 

 distance from the junction of the septa with these portions of the shell, the 

 degree of concavity decreased so as to give a slightly reflexed appearance 

 to the outline of the septa, as seen along these sides in the case of 

 the internal casts of the shell. A similar specimen was found in the up- 

 per shaly courses at Centreville, Ohio. 



In the collection of the Ohio State University is found a fragment of 

 a Cyrtoceras from Brown's Quarry which also possesses an angulate outer 

 and a rounded inner side, compressed lateral sides, a similar siphuncle 

 also within 2 mm. of the outer maigin, and a similar curvature of 

 the septa. The specimen, however, differs widely from the type in the 

 rate of increase of the shell. The fragment which is 55 mm. long, with 

 15 septa, measures 28.5 mm. for its greater diameter at the smaller end and 

 34.5 at its larger extremity. The smaller diameter shows an even "lower 

 rate of increase within this length of shell. The general rate of curva- 

 ture of the fragment is also less. The decreased rate of expansion and 

 the smaller curvature of this Brown's Quarry specimen are, however, 

 only characters which quite commonly belong to the older stages of 

 growth of species of Cyrtoceras, the younger stages of which frequently 

 show more rapid rates of expansion and greater curvature than the later 

 growth, and the Brown's quarry specimen is therefore regarded as repre- 

 senting merely an older portion of the species just described. 



