100 



DESCEIPTIOX OF THE HAED PAETS OF SOME 



' P 



Britain, 

 on the 



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



all Starfishes, is evidently very limited, the prin- 

 cipal Avork of digestion being done by the 

 stomach itself, which folds over the substance 

 to be introduced, and thus gradually dissolves it. 

 The accompanying woodcut (F/'ff. 1) shows 

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

 the plates composing the parts round the acti- 

 nostome and base of the arms. 



This species is conmion to both sides of the 

 Atlantic ; it is found in Norway, Denmark, Great 

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

 east coast of America as far south as Massachusetts Bay. 



Pycnopodia helianthoides. 



Pycnopodia helianthoides Stimps. 1861. Proc. Boston See. Nat. Hist., Vni. 

 Aslerias helianthoides Br. 1835. ProJrom. 



PI. XIII. 



In Pycnopodia the opening at the end of the large ambulacra! plate 

 near the actinostome is best seen in profile {Fig. 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 

 actmal 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 I'eticulated surfaces 

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

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

 nected from the interambulacral system, as can easily be seen by an 

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



* Fig. 1. Crossa.iler papposus. — Internal view, seen from above, the abactinal surface of the plates at 

 the base of one of the arms, round the actinostome, removed, c c, attachment of muscular bands con- 

 necting adjoining ambulacral plates ; a o, a o, openings for passage of ambulacral suckers ; a'b, a'b, am- 

 bulacral plates with projecting spur ; i m, termination of film forming the interbrachial partition ; c'p, spur 

 from interambulacral plates forming connecting floor of actinal surface ; c'J, large muscular plate at base 

 of the arm ; ip, interbrachial plate to which the film forming interbrachial partition is attached (when 

 it extends to that point) at the base of the arms ; s p, spur of interambulacral basal plates forming 

 the base of attachment of the interbrachial partitions ; in p, interambulacral plates forming the so-called 

 mouth-papilla; }>', spines of mp. 



