THE AXIAL CANALS OF THE RECENT PENTACRINI- 



TIDvE. 



By Austin Hobart Clark, 

 Of the United States Bureau of Fisheries. 



The discovery of infrabasals in Metacrinus by Prof. Ludwig Dod- 

 erlein," which was made simultaneously by the present writer ' ; in two 

 other species of that genus and in Isocrinus decorus, has raised an 

 interesting question in regard to the axial canals, through which runs 

 the antiambulaeral nervous system. 



First of all, it may be mentioned that fifteen specimens of Isocrinus 

 decor us have been examined to determine the presence or absence of in- 

 frabasals, which were found in every 

 case; there is no trace whatever of 

 any resorption, and the infrabasals 

 appear to be constantly present in 

 this species throughout life. Also, 

 in six specimens of Metacfhius (five 

 rotundus and one superbus) infra- 

 basals were found as described and 

 figured. Unfortunately, only three 

 specimens of Endoxocrinus parrce 

 ( Pi ntacrinus mulleri of authors) were 

 available for dissection; but all were 

 similar, and in all infrabasals were 

 absent; moreover, the inner ends 

 of the basals had been somewhat resorbed. Tt is possible, therefore, 

 that Endoxocrinus may constantly differ from Metacrinus and Iso- 

 crinus in the absence of infrabasals. 



Reichenspergeiv in \\\> paper on the anatomy of Isocrinus decorus^ 

 gives an account of the axial canals supposedly in that species; un- 

 fortunately, however, the figure he gives represents a specimen of 



"Die Gestielten Crinoiden der Siboga-Expedition, p. 20. 



>> Proc. T'. S. Nat. Mus.. XXXIII, p. 671. 



c Bull. Mus. Comp. Zool., XLVI. No. 10. p. 172 (fig. i». 173). 



Fig. 1. — Diagram showing t ii e 

 codes! of the axial canals in 

 Isocrinus decori s and Metacri- 

 nus rotundus. 



Proceedings U. S. National Museum, Vol. XXXV— No. 1634. 



S7 



