160 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
The Decadocrinidx, his third family, are defined as follows: “Dicyclica, 
in which the arms bifurcate ; each main branch bearing armlets or pinnules ; 
with from none to three anal plates in the dorsal cup, supporting a tube in 
which the lumen is usually flattened transversely, and the plates plicated ; 
with a tegmen composed of numerous small plates, very rarely distinguish- 
able.” The family is said to embrace such forms as Botryocrinus, Bary- 
erinus, Atelestocrinus, Scytalocrinus, and finally Oncocrinus, Eupachycrinus, 
Stemmatocrinus, and Encrinus,—in our opinion the most heterogeneous as- 
semblage of genera imaginable. It is not even true that they all have ten 
main arms; some of them have but five, others seven, nine, twelve, or even 
fourteen; and these modifications apparently occur within the limits of 
a genus, — proof enough that the number of arms is a most unreliable char- 
acter in classification. 
Another objection is that the family includes forms with pinnules and 
without them. Bather’s views respecting the pinnules are rather peculiar. 
He expresses the opinion* that the development of pinnules by itself 
cannot be taken as a character indicative of divergence, and he under- 
takes to prove this by the genus Botryocrinus, of which he asserts that 
“the Swedish species have armlets and not pinnules,” but “the common 
Dudley species undoubted pinnules.” That the appendages of the latter are 
pinnules and not arms, he probably deduced from the fact that the branches 
of this species are somewhat smaller and arranged regularly from alternate 
joints. In discussing the evolution of the arms, Bather assumedf that 
armlets preceded the pinnules, and that when finally the armlets became 
small, ceased to branch, and were regularly placed on alternate sides of 
successive joints, they were called pinnules. This explanation is not satis- 
factory, as it would indicate that the smaller appendages are derived from 
the larger ones. It seems to us more probable that the armlets are true 
arm branches whose development was arrested; and we believe that every 
species of Botryocrinus has armlets, and that pinnules are not represented in 
any of them. otryocrinus decadactylus we take to be morphologically in 
a similar condition to Steganocrinus araneolus (Plate LXI. Fig. 2a); and we 
think that in both of them every joint of the main arms bears an armlet, 
whereas those species of Botryocrinus in which the armlets are given off at 
intervals are in the condition of Steganocrinus sculptus (Plate LXI. Fig. 1 a). 
* Ann. and Mag. Nat. Hist., May, 1890, pp. 873-376. 
+ Ibid., p. 374. 
