﻿422 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



the retractors and sometimes to the end of the body. Allowing for 

 the much greater size of the specimens, the Polian tubules are not 

 quite so well developed as in lissum. The brittle condition of the 

 material makes it difficult to work out details, but the plan is very- 

 similar to that of D. dyscritum. This species appears to be new and 

 may be named: 



DENDROSTOMUM SCHMITTI, new species 



Figure 87, F 



Dendrostomum schmitti differs from D. peruvianum Collin in lacking 

 introvert papOlae, convex trunk papillae, and elevations on esophagus. 

 The nephridia open posterior to the anus, and F^ anchors both the 

 descending and the ascending gut, not the post esophageal gut alone. 

 The relationship of schmitti to peruvianum parallels that of D. lissum 

 to D. zostericolum. 



Between lissum and schmitti the relationship is close; possibly they 

 represent the extremes of geographic variation of one species. 



Type,— U.S. ]<iM. No. 21216. 



Type locality. — Independencia Bay, Peru, lee side of Vieja Island. 



Genus PHASCOLOSOMA F. S. Leuckart 



Phascolosoma F. S. Leuckart, 1828, p. 22, fig. 5. (Type, Ph. granulatum Leuckart.) 

 —Fisher, 1950a, p. 551. 



Phascolosomum Diesino, 1851, p. 63, partim; 1859, p. 758, partim. 



Phascolosoma Keferstein, 1862, p. 39, partim; 1865b, p. 422, partim. 



Phymosomum Quatrefages, 1866, vol. 2, p. 621. 



Phymosonia Selenka and de Man, 1883, p. 54 (emendation of Phymosomum) . 

 Preoccupied by Phymosoma Archiac and Haime, 1850, Description des 

 animaux fossiles du groupe nummulatique de I'Inde . . . , p. 54. 



Physcosoma Selenka, 1897, p. 460. — Spengel, 1898, p. 50. 



Prophymosoma Lambert, 1900, p. 54. 



Physconosoma Bather, 1900, Zoological record, Echinoderms, p. 78. 



Diagnosis. — Tentacles in a single series, forming a crescent or a 

 circle (open dorsally), which is situated dorsal to the mouth and encloses 

 nuchal organ; longitudinal muscle layer of trunk usually split into 

 separate but more or less anastomosing fascicles; usually four retrac- 

 tors, the dorsal and ventral of each side tending to fuse in some species; 

 body covered with papillae fortified by tiny chitinous platelets ; intro- 

 vert hooks, arranged in rings, usually present (not in Phascolosoma 

 antiUarum) ; a dorsal contractile vessel, in most species without villi 

 (present in Ph. antiUarum). 



Remarks. — ^In this genus the arrangement of tentacles is farthest 

 removed from the ancestral type, in which they form a circle sur- 

 rounding the mouth, with the brain and nuchal organ (if present) 

 outside the circle. In Phascolosoma the brain and nuchal organ are 

 situated within the tenacular crown and the mouth is outside and 



