290 TRANSACTIONS OF THE [mAR. 15, 



The spine which is the basis of the foregoing description be- 

 longs to the group which Mr. St. John has associated in his 

 genus Fnigeacanthus, but which in my judgment represents only 

 the body spines of the sharks of which the typical Oraeanthus 

 was the dorsal spine. These abnormal spines are triangular in 

 outline, frequently thin shells, compressed flat in fossilization. In 

 this group we have Oraeanthus pnigeus N. & W., from the 

 Keokuk limestone, 0. abbreviatus N., from the Devonian lime- 

 stone of Ohio and Mr. J. W. Davis has figured several such as 

 forms of Oraeanthus Milleri in his " Fossil Fishes of the Car- 

 boniferous Limestone Series of Great Britain." From the great 

 variety of forms assumed by these defenses in 0. Milleri^ it is 

 evident that the}' were not all fin-spines, but that some of them 

 were scutes somewhat like those of the sturgeon. A part of 

 them, however, viz. : such as that now described, and those 

 figured by Mr. Davis in the work cited above, PI. LXII., figs. 

 3, Y, were probably fin-spines, but not from the back. They are 

 all conical, comparatively short, have a deep sulcus behind, 

 which reaches nearly to the summit, and are uns3'mmetrical. 

 Hence I infer that they are the defenses of the ventral fins, like 

 the short spines of Siethaeanthus descriV)ed in this paper. The^^ 

 might be thought to be pectoral spines like the large and normal 

 spines of Siethaeanthus, with which I have found the fin pre- 

 served in place, but they are not large enough. Oraeanthus 

 Milleri was a large fish of which the dorsal spines were some- 

 times nearly two feet in length, and if the pectoral fins were 

 provided with spines they must have been much larger than 

 those under consideration. 



Ctenacanthus gurleyi, n. sp. 

 (Of this species no figure has been given. — Ed.) 



Spine of large size, ten to twelve inches in length by three to 

 four inches in breadth at the base of the ornamented portion ; 

 section compressed, greatest thickness little more than an inch, 

 enameled surface entirely occupied b}' longitudinal ridges which 

 are of nearly uniform breadth and closelj^ pectinated. 



Up to the present time we have only fragmentary specimens 

 of these great spines. They are manifestly distinct from any 

 species hitherto described and are distinguished above all by 

 their large size, great breadth, flattened sides and numerous sub- 

 equal, closely pectinated costa?. The unornamented portion is 

 remarkabl}' smooth, but its form and dimensions are not shown 

 in the specimens before us. The posterior surface above the 

 opening is flattened with a strong, central, rounded keel. 



