458 BULLETiisr 100, united states national museum. 



semireticulatus^ and ingolfi^ to none of which it is closely related. 

 The following synopsis will contrast the characters : 

 o\ Adambulacral combs with 5 to 7 spines. 



6\ Siiboral spine, when present, slender ; aperture slits small ; no deposits 

 in supradorsal membrane. 

 c\ Paxillae with high pedicel and 5 to 15 spines; R=1.3 r; actinolateral 

 membrane narrow, not defining ambitus; suboral spines always pres- 

 ent pulvillus. 



c*. Paxillae with low pedicel and about 8 spines ; R=1.8 r ; actinolateral 

 membrane defining ambitus; suboral spines absent from some plates. 



corynetes. 

 &^ Suboral spine with 3 sharp edges; aperture slits unusually large; minute 



branched rods in supradorsal membrane temnochiton. 



o". Adambulacral combs with 3 to 5 spines. 



&\ Adambulacral spines usually 3, sometimes 4, short, scarcely projecting 



beyond web ; R=1.4+r rugatus. 



b\ Adambulacral spines 3 to 5, usually 4, projecting far beyond web. 

 c\ R=1.75 r^h ; dorsal membrane thin, evidently reticulated. 



semireticulat-us. 

 c^. R=1.4 r^; ; dorsal membrane thick, not at all reticulate inyolfi. 



Three species are said to lack the suboral spine entirely: ^^er- 

 sonaius, sordidus, and reductus. It is not possible to determine 

 Avhether the three suboral spines in the single specimen of corynetes 

 are abnormally present. The species differs, however, from perso- 

 natus and sordidus in having more numerous adambulacral spines, 

 and from reductus in having only five oral, and fewer paxillar spines. 

 P. sordidus has a straight series of adambulacral spines, the inner 

 4 of the 6 oral spines are webbed independently, and the actino- 

 lateral membrane interradially extends beyond the true margin of 

 the ray. All three forms are from the east Atlantic. 



PTERASTER OBESUS MYONOTUS Fislier. 



Plate 127, fig. 1 ; plate 128, fig. 3 ; plate 133, fig. 4. 



Pteraster obesiis myonotus Fishee, 1916&, p. 28. 



Diagnosis. — Closely related to P. ohesus Clark of Japan and re- 

 sembling superficially P. pulvillus Sars. Differing from ohesus in 

 being nearly pentagonal in form; in having a fairly tough supra- 

 dorsal membrane in which there are well-developed bands of muscle 

 forming a reticulum of hexagons and triangles, and in having fewer 

 paxillar spines. E=28 mm., r=24 mm., E=1.2 r; height of disk 18 

 or 19 mm. 



Description. — The general form is nearly pentagonal, there being 

 only slight interradial indentations, and the disk is thick and cush- 

 ionlike. Supradorsal membrane fairly thick and bristling uni- 

 formly and thickly with the tips of the paxillar spines which raise 

 the membrane or project about 1.5 to 2 mm. above the general level. 



