103 



and thu?^ if the thin shelly membrane, which constitutes the wall of the 

 hjdrospire, were spread out, it would have a width of 22 lines, — and the 

 ten together would form a riband, about 18 inches in length, and nearly 

 two inches wide. The object of the folding is, of course, to confine this 

 large amount of surface to a small space, an arrangement which at once 

 proves the function to be respiratory. Of those figured by Mr. Rofe P. 

 ellipticus Sowerby appears to have only one fold, P. inflatas, id., shows 

 eight folds in one, and eleven in the other hydrospire of the same ambula- 

 crum. Another specimen figured by Mr. Rofe under the name of P. florealis 

 Say, has five folds situated at a distance from the inner surface of the 

 lancet plate as in P. obesus. From the form of the organ I think that 

 Mr. Rofe's specimen cannot be the species called P. florealis by Say. 



If it be granted that these organs are respiratory in their function, then, 

 their five apertures should be called spiracles, — not ovarian orifices." 

 The large anterior aperture would thus be the or o- anal spiracle. Applying 

 this system of terminology to other groups, — the so-called ovarian orifice 

 of the Cystidea, the homologous aperture of JVucleocrinus, Cadaster, Gran- 

 atocrinus and of the Paleozoic Crinoidea generally (but not of the recent 

 forms), should be styled the or o-anal orifice. 



I think that the side of an Echinoderm in which the mouth is situated 

 should be called anterior " even although the anus and the mouth be 

 confluent in one orifice. Most star-fishes have but one aperture for 

 mouth and vent, and yet it is called the mouth by naturalists generally. 

 Why not call the underside of a star-fish " the anal or posterior side," 

 and the central aperture the " anus ?" 



Dr. B. F. Shumard has shown (Trans. Acad. Nat. Sci. St Louis, vol. 

 1, p. 243, pi. 9, fig. 4, ) that in perfect specimens of P. eonoideus Hall, 

 the six summit apertures are closed by several small plates. In a speci- 

 men of the same species sent me by Mr. Lyon, in which those plates e 

 partly preserved, I find that there is a small pore in each of the five 

 angles of the central aperture. The five ambulacral grooves enter the 

 interior through these pores. I have copied his figure but modified it by 

 dding the pores, fig. 63, He also found that the summit of P. sulcatus, 

 Roemer, was covered with an integument of small plates arranged in the 

 form of a pyramid. From these facts he infers that in all the Pcntremites 

 the summit apertures will be found, in perfect specimens, to be closed in 

 a similar manner. 



-5. On the homolofjies of the respiratory organs of the Palcnozoic and 

 recent Echinoderms, and on the Convoluted Plate " of the Crin- 

 oidea. 



In a former note I have advanced the opinion that : — " The grooves on 



