88 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
producing a frayed appearance in that portion of the posterior margin.” 
From C. varians and C. brevis it is distinguished by certain details of 
its ornamentation. In particular, its anterior margin is described as 
bearing a “ prominent, eccentric marginal ridge, from which frequent 
bifurcations are sent off on either side, each offshoot being more atten- 
uated and curved posteriorly on approaching the posterior margin, form- 
ing throughout closely approximated, rounded ridges, of which there 
are about fifty, counting along the inferior margin, and less than half 
that number two-thirds the distance to the apex.” 
There can be no hesitation in referring to this species the original of 
Plate 5, Fig. 1, which is from the same horizon, and belongs to the 
United States National Museum (Cat. No. 4845). This spine displays 
the general outline and ornamentation very satisfactorily, notwithstand- 
ing it has been much laterally compressed by mechanical agencies. It 
has a total length of 15 cm., and maximum breadth of 3 em. A sharp 
and prominent marginal ridge extends for the entire length of the 
anterior border, and forty or more longitudinal costz terminate along 
the very oblique line of insertion. The only noteworthy particular in 
which it differs from the type relates to the ornamentation, which is of 
the decussated instead of the tuberculose pattern. Isolated and well- 
marked tubercles predominate in the type, although it is stated that 
along the anterior margin “they present the appearance of closely 
approximated decussations, apparently the result of abrasion, the 
entire crest of the ridges [cost] being reduced to a smooth polished 
surface.” But in the example before us distinct tubercles are almgst 
entirely wanting, and the costz are crossed by exceedingly numerous 
transverse ridges, the crests of which were apparently sharp and smooth. 
That this difference in ornamental details is of minor importance is 
proved by the conditions existing in C. varians, where tubercles of 
diverse shape are variously disposed in different parts of the spine. 
They frequently surmount the costz in double or even triple rows, and 
the “ pairs of nearly circular tubercles often coalesce, forming a single 
transverse tubercle, which latter is the prevailing, if not persistent form 
in the posterior cost.” 4 
A similar fusion of adjacent tubercles to form 
a single transverse ridge has already heen noticed in C. longinodosus 
(v. supra, p. 80), hence it is not surprising that this process should be 
observed in a varying degree amongst different species, being sometimes 
limited to particular spines of the same species, and sometimes to differ- 
ent portions of a single spine. 
formation and Locality. — Kinderhook Group ; Lowa and Illinois. 
1 Loc. cit. (1875), p. 422. 
4) Se ee _ 
