the Crinoidea, Cystidea, and Blastoidea. 265 



not " ovarian orifices." The large anterior aperture would 

 thus be the oro-anal spiracle. Applying this system of termi- 

 nology to other groups, the so-called ovarian orifice of the 

 Cystidea, the homologous aperture of Nucleocrinus, Codaster^ 

 GranatocrinuSj and of the paleozoic Crinoidea generally (but 

 not of the recent forms) should be styled the oro-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 starfishes 

 have but one aperture for mouth and vent, and yet it is called 

 the mouth by naturalists generally. Why not call the under- 

 side of a starfish " the anal or posterior side," and the central 

 aperture the " anus ?" 



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

 Louis, vol. i. p. 243, pi. 9. fig, 4) that in perfect specimens 

 of P. conoideuSj Hall, the six summit-apertures are closed by 

 several small plates. In a specimen of the same species, sent 

 me by Mr. Lyon, in which those plates are 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 inte- 

 rior through these pores. I have copied his figure, but modi- 

 fied it by adding the pores, fig. lb. He also found that tlie 

 summit of P. siilcatus, Roemer, was covered with an integu- 

 ment of small plates arranged in the form of a pyramid. 

 From these facts he infers that in all the Pentremites the 

 summit-apertures will be found, in perfect specimens, to be 

 closed in a similar manner. 



Dr. C. A. White, at present State Geologist of Iowa, in a 

 paper on the same subject (Bost. Journ. N. H. vol. viii. 

 pp. 481—488), describes P. Norivoodiij Owen and Shumard, 

 and P. stellifornus, id., as having a similar structure ; but he 

 goes further : he considers the central orifice " 7iot to be the 

 mouth ;" and I believe that he is the first naturalist who ever 

 published such an opinion. His idea of its function is thus 

 expressed : — " It seems more probable that, as the ova were 

 germinated within the body, they found their exit througli 

 the central aperture, and were conveyed along the small cen- 

 tral grooves of the pseudambulacral fields before mentioned, 

 beneath the plated integument, to the bases of the tentacula, 

 where they were developed and discharged as in the true 

 Crinoids." I perfectly agree with Dr. White in this view. 

 The central aperture is not the mouth ; in fact, it is not a 

 natural orifice, but a breach in the summit caused by the 

 destruction of a portion of the vault. The true natural orifices 

 of this part are those that I have discovered in P. co7wideus, 

 as above mentioned. They are the homologues of the ovarian 



Ann. d^ Mag. N. Hist. Ser. 4. FoZ.y. 18 



