EASTMAN: CARBONIFEROUS SHARKS. 81 



dorsal fin. From other described species it is readily distinguished by- 

 its peculiar ornamentation. 



The lateral face is ornamented with twenty regularly spaced longitu- 

 dinal costse, which continue perfectly straight without bifurcation, and 

 are surmounted by conical or rounded tubercles separated by intervals 

 equal to their own diameters. Some of the tubercles belonging to the 

 anterior costte show a tendency to become obliquely elongated, as in 

 G. solidus and C decussatus, and those of the posterior costJB are often 

 delicately striated. Xone of the costse exhibit a tendency toward pos- 

 terior deflection, such as commonly occurs amongst other species; and 

 the peculiar beaded appearance of the tubercles is quite remarkable for 

 this genus. The passage of tubercles into transverse ridges, such as 

 we have observed in the newly formed costte of C. longi- 

 nodosus, or in the latest formed portions of older costte, 

 is not evident in the present species, where the primitive 

 tuberculated style of ornament seems to have been per- 

 manently retained. No costte appear along the rounded 

 anterior margin, which has been worn quite smooth prior 

 to fossilization. The spine is preserved for a length of 

 12.5 cm., and the inserted portion has a maximum width 

 of 3.4 cm. The cross-section shown in text-figure 9 is 

 taken across the line of fracture where the rest of the ^^^- '^• 



spine has been broken away ; the width here is 3 cm. and Ctenacanthus 



the thickness 1.4 cm. ^"''"''' ^P- 



1-1 n TIT T^ T • nov. Cross- 



The specific title is bestowed in honor of Mr. J^rederic section of 



A. Lucas, of Washington, to whom the writer is indebted spine. X i- 



for many courtesies, and for the loan of much valuable 



material. The original is preserved in the United States National 



Museum (Cat. No. 4844), and was collected by Mr. L. A. Cox from the 



Kinderhook Limestone, presumably in Iowa. 



Formation and Locality. — Kinderhook Limestone ; Iowa (?) 



Ctenacanthus venustus, sp. nov. 



Plate 3, Fig. 'i. 



Two examples are known of this species, the larger of which belongs 

 to the "Worthen Collection in the Museum of Comparative Zoology, and 

 is selected as the type. The smaller spine, shown in Plate 3, Figure 2, 

 belongs to the United States National Museum (Cat. No. 3385), and 

 was formerly the property of Mr. L. A. Cox, of Keokuk, Iowa. Both 



