268 VERRILL 



fold. One pair of free epioral spines; these are often translucent 

 distally. Supradorsal membrane furnished with a central contractile 

 osculum, guarded by five groups of webbed, projecting spines. It 

 usually contains irregular muscular fibers for its support; muscular 

 bands usually do not form a regular network and are generally very 

 inconspicuous externally. Usually two rows of ambulacral feet, or 

 nearly four-rowed, by crowding, in P. marsippus. 



PTERASTER TESSELATUS Ives. 



Plate xxxn, figures i, 2; plate LXXXVI, figures 4-4^ (details); plate xcvn, 



figure i. 



Pier osier tesselatus IVES, Proc. Acad. Nat. Sci. Philadelphia, for 1888, p. 



421 ; and 1889, p. 169. Fisher, op. cit., 19116, p. 359, pi. civ, figs. 1-5. 

 Pier osier reticulatus VERRILL, op. cit., 19096, p. 555 (an accidental error in 



spelling) . 



A large, plump, five-rayed species, with wide, tapered, subacute 

 rays of short or moderate length, and with high, rounded margins to 

 the disk. 



The ambulacral grooves are turned up a little at the end of the 

 rays, so that the distal and apical plates are dorsal. Submarginal 

 fold narrow. 



Radii of the largest (dry) specimen from Puget Sound (Prof. 

 Trevor Kincaid) are 42 mm. and 70 mm. to 75 mm. ; height, 50 mm. 

 Radii of one from off Sidney, British Columbia, are 28 mm. and 

 40 mm. ; height, 35 mm. The alcoholic specimen figured, from the 

 Harriman Expedition, is larger, the greater radius measuring 90 mm. 

 or more. 



The dorsal surface is covered with a strong, thick, supradorsal 

 membrane, through which the spinules of the pseudopaxillae usually 

 show only as very small points, arranged in a complex reticulated 

 pattern. But in the largest dry specimens they appear as small, more 

 elevated, obtuse spines or tubercles, sometimes showing a stellate 

 arrangement, but more often closely reticulated or areolate. The 

 dorsal osculum is relatively rather small, with elevated spinose mar- 

 gins, the spines not very long, rather stout, the points not pro- 

 jecting beyond the webs. 



The adambulacral fans of spines consist of about three or four 

 outer, rather long, nearly equal, slightly tapered spines, and two 

 much smaller inner ones, of which the innermost is only about one- 

 fourth as long as the outer ones, and the next one is about half their 

 length. In some large specimens these spines become clavate. 



