90 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
culation of the coste, 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 C. varians and 
C. spectabilis from the Kinderhook, 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, 
Towa. 
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. deflexus, 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 Zodlogy 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] costz. 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 
coste, 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 the line of inser- 
tion. The present species has a more rounded anterior margin (ef. text- 
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