90 bulletin: museum of comparative zoology. 



dilation of the costse, and it is evident that the latter increased by- 

 bifurcation, and were much deflected along the posterior margin. These 

 conditions are characteristic of the group represented by (7. varians and 

 C. spcctabilis from the Kinderliook, which was most prolific at the 

 beginning of the Lower Carboniferous, and entered almost immediately 

 thereafter upon its decadence. 



Formation and Locality. — Upper Burlington Group; Burlington, 

 Iowa. 



Ctenacanthus solidus, sp. nov. 



Plate 7, Figure 3. 



Type. Spine referred to the posterior dorsal fin : United States 

 National Museum. 



Three spines from the Kinderhook of Iowa have come under the 

 ■writer's observation, which belong to the group represented by C. 

 varians, C. spectabilis, C. dejlexus, etc., and yet differ from all these in 

 certain details by which they may be specifically distinguished. Two 

 of these specimens belong to the United States National Museum, the 

 more perfect of which bears the catalogue number 3383, and is selected 

 as typical. The smaller spine is shown nearly of the natural size in 

 Plate 7, Figure 3, and is catalogued as number 4843. The third speci- 

 men referred to forms part of the A. H. Worthen Collection in the 

 Museum of Comparative Zoology at Cambridge. 



The spines referred to this species are very similar in proportion 

 and general outline to those of C. spectabilis, but their ornamentation 

 is coarser, and there are fewer longitudinal costse. These do not exhibit 

 the abrupt posterior deflection on approaching the line of insertion, 

 which is so conspicuous a feature of C. spectabilis and C. varians., and 

 the line itself is shorter and less oblique than in those forms. The 

 costse, in addition, are occupied in the present species by prominent, 

 well-separated tubercles, which may be either rounded or obliquely 

 elongated, and whose summits are distinctly wrinkled or striated. An- 

 other distinguishing character is furnished by the anterior margin. In 

 C. spectabilis this is more or less angular, and bears a prominent sharp 

 ridge, from which ''frequent bifurcations are sent off on either side, and 

 these again bifurcate descending, each offshoot being more attenuated 

 and curved posteriorly on approaching the posterior margin," forming 

 in all about fifty rounded ridges to be counted along tlie line of inser- 

 tion. The present species has a more rounded anterior margin (cf. text- 



