348 THE CANADIAN NATURALIST. [Vol. vi. 



the pectinated rhombs of Cystideans, the tube apparatus of Pen- 

 tremites, and the sand-canal of Asterids. Messrs Meek and 

 Worthen and Dr. Liitken, on the other hand, regard it as asso- 

 ciated in some way with the alimentary canal and the function of 

 nutrition. 



The author strongly supported the latter opinion. The peri- 

 visceral membrane in Antedon and Pentacrinus already alluded 

 to, which lines the whole calyx, and whose involutions, support- 

 ing the coils of the alimentary canal, contribute to the formation 

 of the central columella, is crowded with miliary grains and small 

 plates of carbonate of line; and a very slight modification would 

 convert the whole into a delicate fenestrated calcareous plate. 

 Some of the specimens in Mr. AVachsmuth's collection show the 

 open reticulated tissue of the central coil continuous over the 

 whole of the interior of the calyx, and rising on the walls of the 

 vault, thus following almost exactly the course of the perivisceral 

 membrane in the recent forms. In all likelihood, therefore, the 

 internal calcareous network in the crinoids, whether rising into a 

 convoluted plate or lining the cavity of the crinoid head, is simply 

 a calcified condition of the perivisceral sac. 



The author was inclined to agree with Mr. Eofe and Mr. Bil- 

 lings in attributing the functions of respiration to the pectinated 

 rhombs of the Cystideans and the tube apparatus of the Blastoids. 

 He did not see, however, that any equivalent arrangement was 

 either necessary or probable in the crinoids with expanded arm, 

 in which the provisions for respiration, in the form of tubular 

 tentacles and respiratory films and lobes over the whole extent of 

 the arms and pinnules, are so elaborate and complete. — Abstract 

 of a paper 7'ead before the Royal Society of Edinburgh^ by Prof. 

 Wyville Thomson, April 3, 1871. From " Nature.'' 



On the supposed Legs of the Trilobite, Asaphus pla- 

 TYCEPHALUS. By James D. Dana. — (Am. Jour. Sci. May, 

 1871 .) * At the request of Mr. E. Billings of Montreal, I have 

 recently examined the specimen of Asaphus platycephalus be- 



* In the last number of this Journal, p. 227, an abstract from the 

 Report of the Committee of the Brit. Association on Fossil Crustacea 

 was published, and this paper should have appeared at the same time. 

 In the March number of the Am. Jour. Sci., Prof. Dana has given a 

 second notice, in reply to Mr. Woodward. We shall publish them 

 both together. 



