456 BULLETIiSr 100, UNITED STATES NATIONAL MUSEUM. 



to the plate at mouth of ambulacral furrow; the mouth spines are 

 13 or 14 instead of 8, and the outer spines form a fascicle on the sur- 

 face of the plate near the margin, instead of a series, without a web, 

 on the margin. The apophysis of the adambulacral plate, in Tiiedusa, 

 has 1 long spine; in sol^ 3. There seems to be a difference in the 

 form of the plates of the abactinal and lateral surfaces of the body, 

 but it is not possible to determine how constant this is. 



The family Myxasteridae includes only 3 genera, Myxaster^ Asthe- 

 nactis^ and Pythonaster.'^ 



Family PTERASTERIDAE Perrier. 



Genus PTERASTER Miiller and Troschel. 



Pteraster Mullee and Troschel, 1842, p. 128. Type, P. 7nilitaris (O. F. 

 Miiller). 



PTERASTER CORYNETES Fisher. 



Plate 127, figs. 2, 3 ; plate 128, fig. 1 ; plate 133, figs, 5, 5a. 

 Pteraster corynetes Fisher, 19166, p. 28. 



Diagnosis. — Abactinal surface resembling superficially that of 

 P. pulvillus; probably more nearly related to P. semireticulatm. 

 Paxillae with low pedicel surmounted by 7 or 8 longer, radiating, 

 peripheral spinelets surrounding a central shorter one ; tips of periph- 

 eral spinelets united by fibrous tissue; spiracula in lines between 

 spinelets; no deposits in supradorsal membrane; furrow fans with 7 

 spines (distally, 6) ; actinolateral spines stout, the tips defining am- 

 bitus ; 5 oral spines, the 10 united by a continuous membrane ; suboral 

 spine may be entirely lacldng; when present, slender, tapering. Pays 

 5; R=24 mm., r=13 mm., R=1.8 r; breadth of ray of base, 14 or 15 

 mm. ; thickness of disk, 9 mm. 



Description. — Abactinal surface resembling somewhat that of P. 

 pulvillus and also that of P. semireticulafus. Supradorsal mem- 

 brane very thin, so that the 7 or 3 widely radiating peripheral spine- 

 lets of each paxilla can be easily seen, a much shorter erect spinelet 

 occupying the center of each circle. The paxillae, in consequence, 

 have a stellate appearance, and a peripheral fibrous band connects 

 the tips of all the spinelets (except the central), marking off the 

 abactinal surface into areas, somewhat as in semireticulatus., but 

 these bands are not at all conspicuous, except on the sides and outer 

 half of ray. Between any 2 radiating spines is a linear series of 4 

 to 7 spiracula, usually quite small. Pedicel of paxillae short and 

 stout on the rays, being about half the length of the peripheral spine- 

 lets, which are also stout, and tapered from the truncate, minutely 

 denticulate lip toward the base. They resemble little clubs with 



5 



iVerrlll, 1914a, p. 204, has made a special family of Pythonaster, but without diag- 

 nosis. I do not know in what particulars, therefore, it differs from the Myxasteridae. 



