REPORT ON THE CRINOIDEA. 177 



Measurements B represent the results of a similar comparison of the yet more robust 

 Antedon tenella from the West Atlantic with other immature examples of Antedon 

 prolixa, larger than that already considered, but absolutely smaller than the individual 

 of Antedon tenella with which they are compared. In each case alike the cirri of 

 Antedon prolixa with an incompletely developed calyx and arms, are longer and have 

 more numerous joints than individually larger examples of Antedon tenella. The 

 difference in absolute size may be judged from the fact that in Antedon prolixa (B) 

 there is a length of but 4'5 mm. between the pinnule on the seventh and that on the 

 thirteenth brachial ; while in Antedon tenella this distance measures 7 mm., and yet the 

 cirri of this latter type are not much more than half the length of those of the young 

 Antedon 2^'olixa. 



The reverse is the case with the pinnules, however ; the first pinnule of Antedon 

 tenella has nearly forty joints, and reaches 15 mm., while that of the young Antedon 

 prolixa, 10 mm. long, has but twenty-seven joints, though its cirri are so much better 

 developed than those of the other species. 



It will, I think, be evident from the above-mentioned facts that Antedon tenella and 

 Antedon prolixa are different species, and not merely different stages of growth of one 

 and the same type, as supposed by Fischer. The most robust examples of Antedon tenella 

 with fully-developed arms and pinnules have very distinctly smaller cirri than immature 

 and absolutely smaller examples of Antedon prolixa. This demonstrates the fallacy of 

 Fischer's conclusion, which he further endeavours to support by the following passage : — 

 " Sollten noch irgend welche Zweifel entstehen, so werden dieselben wiederlegt durch die 

 Thatsache, class ich gleichzeitig mit den bereits beschriebenen Exemplaren zwei Penta- 

 cfinus-&ta,dieu auf einer Rhynconella aufsitzend fand, die volkommen mit den Beschrei- 

 bungen tibereinstimmen, die Sars in seinen ' Memoires des crinoides vivants ' gibt, und 

 auf Taf. v und vi abbildet." 



I must confess that I cannot see the force of this reasoning. Fischer found two 

 examples of Antedon prolixa at Jan Mayen, and two smaller forms, together with two 

 Pentacrinoids, all four of which he referred to Antedon sarsii (tenella). But I do not 

 understand at all why the occurrence of these two Pentacrinoids ' should render it so 

 certain that Antedon tenella is only an immature Antedon prolixa. Precisely the same 

 reasoning would entitle me to assert that Antedon tenella is only an immature form of 

 Antedon eschrichti. For the latter species was dredged by the " Porcupine " in the 

 cold area together with Antedon tenella and its Pentacrinoid ; and in like manner 

 Antedon rosacea was obtained on the Skerki Bank together with Antedon phalancjium 

 and its Pentacrinoid. Antedon midtispina with three Pentacrinoids was dredged by 

 the Challenger at the same Station (No. 344) as Antedon porrecta ; while Antedon 



1 I cannot help suspecting that there may be differences between these Pentacrinoids and the larva of Antedon 

 tenella which have escaped Fischer's notice. 



(zoou chall. exp. — part lx. — 1887.) Ooo 23 



