232 Messrs. R. Etherlclge, Jun., and P. H. Carpenter on 



thin sections for the microscope, '' that the ridges on tlie 

 striated interradial surfaces are the tops of a series of folds of 

 a thin test or membrane, the alternate folds being so united at 

 the ends as to form a series of long but very narrow sacs ;" and 

 he further suggested their respiratory cliaracter *. These 

 organs were called hydrospires by Billings f, who has con- 

 firmed Rofe's observations ; and after a careful examination 

 of Rofe's material, we are glad to be able to add our own 

 testimony as to the accuracy of his descriptions. The full 

 complement of hydrospires is deficient, as Mr. Billings has 

 very justly pointed out, by two sets, in consequence of one 

 interradius being completely occupied by the large vent + ; 

 there are therefore eiglit sets, instead of ten as in the closely- 

 allied Phfenoscliisma, Pentremites, and other genera. Owing 

 to the direct communication of the hydrospire-slits with the 

 exterior, there are no hydrospire-canals or spiracles. 



From an examination of the British Cadasters we can con- 

 firm the description given by Billings of the structure of the 

 ambulacra in a Canadian species §. As there are no hydro- 

 spire-canals, there are no pores ; and we doubt whether outer 

 side plates are present in all species. Although we agree 

 with most of Billings's descriptions of structural characters, 

 we cannot accept his deductions from them as to the Cystid 

 affinities of Cadaster , a point Avhich we shall touch upon later. 



Messrs. Meek and Worthen have suggested || that the 

 puncta in the hydrospiral grooves communicate directly with 

 the hydrospires, and represent the spiracles of other Blastoids. 

 We cannot assent to this ; nor are we at all clear that puncta 

 exist in the impressed lines on the interradial areas of 

 Codaster. M'Coy only described them with doubt ; and no 

 definite evidence has presented itself amongst the large num- 

 ber of British specimens of Codaster examined by us. 

 Neither do we sec the slightest reason to sup])ose that any 

 portion of the hydrospire-apparatus was capable of movement, 

 as suggested by the following remark of S. S. Lyon % : — 

 " these pieces were evidently capable of being compressed and 

 depressed." 



The number of hydrospires varies considerably according 

 to species. In M'Coy's C. trilobatus there are as many as 



* Geol. Mag. I860, ii. p. 251. 



t Amer. Journ. He. 18G9, xlviii. pp. 78-80. 



X Loc. cit. 1870, xlix. p. 54. 



§ Loc. cit. 1809, xlviii. p. 79. 



II Proc. Acad. Nat. Sci. Pbilad. 1869, p. 84 (note). 



^ D. ].). Oweu's 3rd Report Geol. Survey of Kentucky, 1857, p. 494. 



