100 



DESCiaPTIO:N^ OF THE HARD PAETS OF SOME 



Britain, 



^'^" ^* surrounding the mouth ; though their use, as in 



all Starfishes, is evidently very limited, the prin- 

 cipal work of digestion being done by the 

 stomach itself, which folds over the substance 

 to be introduced, and thus gradually dissolves it. 



The accompanying woodcut (Fi(/. 1) shows 

 somewhat more plainly than Fi(/. 3 on PL XII. 

 the plates composing the parts round the acti- 

 nostome and base of the arms. 



This species is common to both sides of the 

 Atlantic ; it is found in Norway, Denmark, Great 

 on the west coast of France, in Ireland, Greenland, and extends 



on the east coast of America as far south as Massachusetts Bay. 

 Pycnopodia helianthoides. 



Pycuopodia /irliani/ioides Stimps. 1861. Proc. Boston Soc. Nat. Ilist., VIII. 

 Aslerias helianthoides Bu. 1835. rrodroin. 



p/. xni. 



In Pycnopodia the opening at the end of the large ambulacral plate 

 near the actinostome is best seen in profile {Fi(/. 2) ; it differs in no 

 way from the structure of the corresponding plates in Asteracanthion, 

 though apparently, on first examination, the actinal plates forming the 

 actinal ring seem quite peculiar, owing to the disappearance near the 

 mouth of the interbrachial membrane, and the isolation of the interbra- 

 chial partition ; this connects the actinal and abactinal reticulated surfaces 

 by a mere film only. The large plate at the actinal ring, forming the 

 base of the interbrachial partition (PI. XIII. F/(/. 6 i p), is entirely discon- 

 nected from the interambulacr.il system, as can easily be seen by an 

 examination of the actinal extremity of the arm from the inside of 



* Fig. 1. Crosmstcr pappoxiis, — Internal view, seen from above, llic abactinal surface of the plates at 

 tlic base of one of (be arms, round the actinostome, removed, c c', attachment of muscular bands con- 

 ncctin;; adjoiiiii);^ aniliulairal plates; u o, (i o, openings for passage of ambulacral suckers ; a '6, o '6. am- 

 bulacral plates with projcclinj; spur; i m, termination of fdm forming the interbrachial partition; c'p. spur 

 from intcrand)ulacral plates forming connecting floor of actinal surface; c'fe, large muscular plate at base 

 of the arm ; t p, interbracliial plate to which the film forming intci'brachial partition is att^iched (when 

 it extends to that point) at the base of tbe arms; s/), spur of intcrambulacral basal plates forming 

 the base of attachment of the interbrachial partitions ; m p, intcrambulacral plates forming the so-called 

 raouth-papillic ; ;/, spines of mj^. 



