120 BULLETIN OF THE 
ECHINARACHNIUS PARMA Gray. 
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 EKchinarachnius. The pluteus of 
Arbacia is known, that of Strongylocentrotus ¢ 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. Ina paper on the embryology of the genus Arbacia, I have 
described ||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,” { Z. parma, resembles in many respects that of Arbacia.** The 
* Ueber die Gattungen der Seeigellarven. Siebente Abhandlung iiber die Meta- 
morphose der Echinodermen. Abdh. k. preus. Akud. d. Wiss. Berlin, 1856. 
+ Revision of the Echini. Mem. Mus. Comp. Zadl., III. p. 730. 
t The pluteus of Strongylocentrotus must be rare at Newport. I have not 
recognized it in my fishing there in several summers. 
§ Op. cit., Pl. XII. Embryological Monographs, No. 2. Mem. Mus. Comp. Zoil., 
Vol. IX. No. 2. 
|| On the Development of the Pluteus of Arbacia. Mem. Peabody, Acad. Sci., 
I. 6, 1881. 
4] Many genera of Clypeastroids, besides Echinarachnius, are also called sand- 
dollars from the shape of the adult. In the South Mellita bears that name. 
Echinarachnius is sometimes called the sand-cake, in New England coast towns. 
** For a history of the development of Arbacia see A. Agassiz, Revision of the 
Echini, pp. 729, 733-735. E. Selenka, Keimblatter u. Organenlage der Echini- 
den. Zeit. f. Wissensch. Zool. XXXIII. Pl. VIL, Figs. 84-37. J. Walter Fewkes, 
On the Development of the Pluteus of Arbacia. Jem. Peabody Acad. Sci. I. 
