160 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



The Decadocrinidse, 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- 

 crinus, Atelestocrinus, Scytalocrinus, and finally Oncocrinus, Eupachycrinus, 

 Stemmatocrinus, and Bnerinus, — 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 assumed! 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. Botryocrinus decadactylus we take to be morphologically in 

 a similar condition to Steganocrinus araneolus (Plate LXL Fig. 2 a) ; and we 

 think that in both of them every joint of the main arms bears an armlet, 

 whereas those species o^ 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. 373-376. 

 t Ibid., p. 374. 



