120 BULLETIN OF THE 



ECHINARACHNIUS PARMA Gbay. 

 General Notice. 



Our knowledge of the development of Echinarachnius is small. 

 Johannes Miiller* long ago described a pluteus which he referred to 

 Echinocyamus. From its likeness to the pluteus described by Miiller, 

 ■which is a very characteristic one, A. Agassiz suggested t that the com- 

 mon Newport pluteus is the young of Echinarachnius. The pluteus of 

 Arbacia is known, that of Strongylocentrotus X is characteristic, and 

 Mr. Agassiz was led to refer a pluteus, which is neither of these, and 

 which is found in great numbers in Narragansett Bay, to the young 

 of Echinarachnius. No one has up to the present brought forward any 

 observations bearing on this suggestion. I have raised the egg of Echin- 

 arachnius into a pluteus, which is closely allied to his, and have raised 

 plutei which are identical into a young stage of Echinarachnius. The 

 plutei described by A. Agassiz are not mature. A. Agassiz has also 

 figured § the young stages of Echinarachnius after the absorption of the 

 pluteus. In a paper on the embryology of the genus Arbacia, I have 

 described II the peculiar pigmentation on the viscous covering of the egg 

 of the Echinarachnius while in the ovary. 



These contributions constitute the greater part of our knowledge of 

 the development of Echinarachnius. 



The development of the pluteus of the " sand-cake " or " sand-dol- 

 lar," IT E. parma, resembles in many respects that of Arbacia.** The 



* Ueber die Gattungen der Seeigellarven. Siebente Abliandlung iiberdie Meta- 

 morphose der Echinodermen. Abh. k. preus. Akad. d. Wiss. Berlin, 1855. 



t Revision of the Echini. Mem. Miis. Comp. ZdoL, III. p.~730. 



t The pluteus of Strongylocentrotus must be rare at Newport. I have not 

 recognized it in friy fishing there in several summers. 



§ Op. cit., PL XII. Embryological Monographs, No. 2. Mem. Mus. Comp. ZooL, 

 Vol. IX. No. 2. 



II On the Development of the Pluteus of Arbacia. Mem. Peabody, Acad. Sci., 

 L 6, 1881. 



IT Many genera of Clypeastroids, besides Echinarachnius, are also called sand- 

 dollars from the shape of the adult. In the South Mellita bears that name. 

 Eciiinarachnius is sometimes called the sand-cake, in New England coast towns. 



** For a history of the development of Arbada see A. Agassiz, Revision of the 

 Echini, pp. 729, 733-735. E. Selenka, Keimblatter u. Organenlage der Echini- 

 den. Zeit. f. Wissensch. ZooL XXXIII. PI. VII., Figs. 34-37. J. Walter Fewkes, 

 On the Development of the Pluteus of Arbacia. Mem. Peabodi/ Acad. Sci. L 



