Mr. E. Billings 07/ the Structure qft/ie Crinoidca (Cr. 40!) 



XLVII. — Notes on the Structure of the Crinoidca, Cystidea, 

 and Blastoidca, Bj E. BiLLrxciS, F.G.S., Palaioiitologi.st 

 ot" the Geological Survey of Canada*. 



[Continued from p. 20G.] 



5. On the Homologies of the Resjnratory Organs of the Palcco- 

 zoic and Recent Echinodernis^ and on the " Convoluted 

 Plate'''' of the Crinoidea. 



In a former note I have advanced the opinion that " The 

 grooves on the ventral disk of Cgathocrinus, and also the in- 

 ternal ' convoluted plate ' of the pah^ozoic Crinoids, with the 

 tubes radiating therefrom, belong to the respiratory and per- 

 haps, in part, to the circulatory systems — not to the digestive 

 system. The convoluted plate, with its thickened border, 

 seems to foreshadow the ' ccsopluigeal circular canal,' with a 

 pendent madreporic apparatus as in the llolothuridea " 

 {ante^ p. 255, note.) I should liave refeiTcd it to the ma- 

 dreporic system of the existing Echinodermata in general, 

 instead of to that of the Holothuridea in particular. At 

 the time tlie note was written I had in view the nuidreporic 

 sac of llolothuria, which, as will be shown further on, most 

 resembles in form that of Actinocrinus. The figures and 

 descriptions which follow are intended to show the gradual 

 passage or conversion of the respiratory organs of the Cystidea, 

 Blastoidca, and Palaiocrinoidea into the ambulacral canal- 

 system of the recent Echinoderms, and that, as the convoluted 

 plates of the former have the same stiiicture and connexions 

 as the madrej)oric sacs and tubes or sand-canals of the latter, 

 they are most probably all the homologues of each other. 



Among the Cystidcans we find several genera, such as Cri/p- 

 tocrinites, Malocystites, Trochocgstites, and apparently some 

 others, whose test is totally destitute of respiratory pores, being 

 composed of simple solid plates like those of the ordinary 

 Crinoidea. In a second group of genera, among which may 

 be enumerated Cargocgstites, Echinosphoirites, Pahvocystites^ 

 and Protocysfites, the whole of the external integument seems 

 to have been respiratory, as all or nearly all of the plates of 

 which it is composed are more or less occupied by variously 

 arranged poriferous or tubular structures. The Cystideans of 

 these two groups hold the lowest rank of all those known. In 

 their general structure they are mere sacs, of a globular, 

 ovate, or (as in the case of Trochocystite^) flattened form. 

 Their test consists of an indefinite number of plates without 

 any radiated arrangement. They were also, according to our 

 present knowledge, the first to make their appearance, two of 

 * From Silliman's American Journal of Science, January 1870. 



