182 BULLETIN OF THE 



is therefore of some importance as tending to indicate the specific 

 identity of the examples from these two locaHties. In most specimens 

 the spots are confined to the pinnules of the hinder arms, sometimes to 

 one or two arms only ; but in one case I found them on all the arms 

 except the two immediately adjoining the mouth. As a general rule, the 

 arms distinguished by their presence are of the ungrooved type, to which 

 I have already called attention.* In some specimens the dimorphism 

 of the arms is exceedingly marked, just as in Ad. ivAymorpha. The 

 anterior arms are long, slender, and composed of many joints bearing 

 similar long and slender pinnules ; while the hinder arms are shorter, 

 fewer-jointed, and much more fleshy, with stouter pinnules, in which the 

 genital glands are better developed than in the pinnules of the anterior 

 arms. These are grooved and tentaculiferous, while the hinder arms 

 have no ambulacral groove nor tentacles, and the pinnules ai'e usually 

 spotted with the "sense-organs." These may occur in Ad. meridionalis 

 as early as the 10th pinnule of the arm, while in Ad. poli/morjjha I have 

 rarely found them lower than the 2.5th pinnule. 



In Ad. meridionalis, as in all species of which I have been able to 

 examine any considerable number of individuals, the presence of un- 

 grooved arms and of " sense-organs " is altogether inconstant and irreg- 

 ular. But though it is in this way merely a potential character, it is 

 one which is peculiar to Adinometra, and is therefore of some systematic 

 value. On the other hand, there is a similar potential character, which 

 so far as I have yet seen is peculiar to Aniedon, though it appears to be 

 constant in Pentacrinus. This is the existence of a complete calcareous 

 plating at the sides of the ambulacra on the arms and pinnules. Many 

 of the Antedon species dredged by the " Challenger " in the Pacific re- 

 semble Pentacrinus in having a very complete anambulacral plating on 

 the disk ;f while there is a double row of plates along each side of the 

 ambulacra of the arms and pinnules, especially of the latter. The side 

 plates rest on the pinnule joints and support the covering plates, which 

 can be made to overlap one another from opposite sides so as to close in 

 the groove completely. $ Several of the " Blake " /l«'/ecZo;K'!, including 

 Ant. sjjinifera, exhibit these peculiarities better than some Pentacrinus 

 species do. But I have never yet found them in any Adinometra. There 

 are many species, such as Act. pulchella and Act. granidifera Pourt. sp., 



* Actinomdra. Trans. Linn. Soc, Sec. Ser., Zool., Vol. IL pp. 31-41, PI. IL 

 Figs. 3-6. — Popular Science Review, X. S., Vol. IV. pp. 195, 199, PI. VL Figs. 1, 2. 

 t Proc. R. S., 1879, pp. 388, 389. 

 t Popular Science Review, N. S., Vol. IV. pp. 195, 196, PI. VL Figs. 10, 12. 



