261 



December 4, 1861. 



Dr. C. T. Jackson, Vice-President, in the chair. 



The following papers were presented : 



Ox NEW Gexera and Species of Starfishes of the Family 



Pycxopodid^* (Asteracanthiun Mull, and 



Trosch.) By William Stimpsox. 



Genus Pycnopodia Stm. 



Body depressed, multiradiate ; rajs equal ; disc very broad, but 

 with the inter-radial septa of its cavity extending inward quite to the 

 mouth, and nearly reaching the walls of the stomach; septa thin, 

 with only minute scattered calcareous deposits, but strengthened 

 near their sharp inner edges by a flexible, perpendicular band of 

 articulating feathered plates. Dorsal skin very sparsely provided 

 with calcareous matter, containing only a few small scattered tergal 

 ossicles, bearing slender spines. On the back of the rays these ossi- 

 cles are rounded and entirely isolated, but on the disc they are some- 

 times connected by a thin deposition of calcareous matter. Ambulac- 

 ral furrows very broad, with the pores in four rows, except at the 

 base, where they form only two rows. Interambulacral ossicles 

 strongly developed and very regular in their arrangement ; those of 

 the outer row trilobate, closely approximated, and imbricated. One 

 madreporic plate. Papulae f in clusters. 



The type of this genus, and the only species known, is — 



Pycxopodia heliaxthoides. 

 Asterias helianthoides Brandt, Prodr. desc. anim. Mertens. p. 71. 

 It is found on the shores of Oregon and California. 



Genus Asterias Lin. 

 The reasons for retaining this ancient name for the typical Astera- 

 canthia of Miiller and Troschel are discussed at length in the mono- 

 graph. A. rubens may be considered its type. 



* Miiller and Troschel give, as the essential and distinctive character of this 

 family, " ambulacral feet in four rows;" all other true Starfishes having only two 

 rows. But the increased number of rows is simply the result of the crowding ne- 

 cessary for the arrangement of the more numerous feet possessed by some of the 

 species. We have Astemcanthia, with only two rows (not, however, exactly recti- 

 linear), and others with six or eight more or less distinct rows near the base of 

 the ray. We have named a genus Pycnopodia, in order to secure an appropriate 

 name for the family. 



t By the term " papulfe " we have designated those delicate closed vesicles, or 

 protrusions of the internal lining membrane, which project from the pores among 

 the tergal and interambulacral plates, and which are generally, but incorrectly, 

 termed "dorsal feet." We have rejected the term ••papillae," because this has 

 been frequently applied to the ambulacral spines. 



