233 
III. Thenarocrinus callipygus. 
a Family Carabocrinid^e, characterized by the presence in 
the basal circlet of a radianal or part of one, is a different 
matter. The Fistulata are now so well known that their 
classification must depend on the question of descent. In the 
present instance, however, this question is obscured, partly 
because so few species of the genera in question are known, 
but chiefly because those genera are early forms but a little way 
removed from the common parent stock. Garabocrinus , for 
instance, seems related to Euspirocrinus , of which genus a 
species, E. obconicus , has been found by Mr. W. R. Billings* 
in the Trenton Limestone. Thenarocrinus also presents some 
points of resemblance to Euspirocrinus , especially in the arms, 
in the general shape of the dorsal cup, and in the column. 
But both Carabocrinus and Euspirocrinus are very closely 
connected with Ottawacrinus and with early species of Den - 
drocrinus . In fact, were we to consider Ordovician forms 
alone, we should undoubtedly place all these genera in one 
Family. Clearly, however, this would not be satisfactory ; 
the evolution of that assemblage did not cease, and the ques- 
tion is — Can we discern more than one line of evolution ? 
Certainly there seem to be three divergent lines ; and the 
fact that two of these (the Carabocrinidse and Euspirocrinidse) 
soon appear to reach their termini does not impugn their 
existence. 
Undoubtedly the establishment of a Family Carabocrinidse 
would appear more reasonable if we could trace its descent 
rather further than is at present possible, but among forms 
reckoned as Fistulata the descendants of Thenarocrinus are 
still to seek. There is, however, a likeness so remarkable 
that it cannot be overlooked. The resemblance of Thenaro- 
crinus to Enallocrinus may be superficial, but, except for the 
anal structures, it is very complete. The plates of the dorsal 
cup, other than anals, are the same in number and in shape, 
and the following sentences from the most recent description 
of Enallocrinus f apply almost equally well to Thenaro- 
crinus : — u First radials wide, their distal faces usually occu- 
pied by a deep lunate excavation in which the second primary 
and one or two higher radials rest; sometimes, however, 
truncate.” u Rays completely disconnected from the first 
radials up, and the arms becoming free variously between the 
first to the fourth bifurcation. Second radials [i. e. first 
costals] perforated by a large axial canal which passes down- 
ward ; it ramifies within the higher radials, and passes into 
* Trans. Ottawa Field Naturalists’ Club, ii. no. 2, 1885. 
t Wachsmuth and Springer, u Crotalocrinus : its Structure and Zoolo- 
gical Position,” Proc. Acad. Nat. Sci. Philadelphia, 1888, pp. 387, 388. 
