232 BULLETIN 82, UNITED STATES NATION.VL MUSEUM. 



There appear to be no deposits in the tentacles. 



Nemaster grandls. — Each ambulacral lappet contains a large and conspicuous 

 plate, very thin and delicate, triangular in shape with the outer apex rounded 

 and somewhat produced. There are about three of these to a pinnular. 



Nemaster iowensis. — Each ambulacral lappet contains a large and conspicuous 

 triangular plate, there being about three of these to a pinnular. 



It was in this species that an ambulacral skeleton was first noticed in the 

 family Comasteridffi. The deposits were described and figured by Mr. Frank 

 Springer in 1903. 



Nemaster ruhiginosa (fig. 781, p. 366). — Each ambulacral lappet contains a 

 very thin and delicate consi^icuous large, rounded, triangular plate, of which there 

 are about three to a pinnular. 



Nemaster discoidea. — I have been unable to detect any calcareous deposits in 

 the brachial or pinnular perisome of this species. 



CoTnissia feregrina. — There appear to be no calcareous deposits in the brachial 

 or pinnular perisome of this species. 



Comissia liitkeni. — The lateral perisome of the pinnules in this species is 

 almost naked, containing merely a few very slender and inconspicuous usually 

 widely scattered spicules. 



The spicules in the tentacles are very highly developed, forming a continuous 

 layer along the outer side, reaching nearly to their tips. 



Commisia littoralis. — The lateral perisome of the pinnules and the ambulacral 

 lappets contain a great number of scattered minute spicules which become longer in 

 the latter. In lateral view these spicules are seen to form bands from the lappets 

 to the border of the pinnulars, where they intermingle with another band of very 

 minute spicules running along the latter. 



There are no spicules in the tentacles. 



LeptoneTnojster venustus (fig. 783, p. 366). — In the lateral perisome of the 

 pinnules are slender, very delicate, and more or less irregular, sometimes branched, 

 rods, evenly spaced, lying at right angles to the border of the pinnulars, some- 

 times in groups of two or three, about three (or three groups) to a pinnular. 

 Occasionally these become more numerous, forming a very loose and rudimentary 

 narrow crescentic meshwork about the distal border of the marginal lappets. 



The spicules in the tentacles are unusually abundant and often form along 

 the distal side a continuous meshwork reaching nearly to the tip. 



Comatonia cnstata (fig. 790, p. 372). — The lateral perisome of the pinnules 

 contains a series of straight and simple very slender rods leaning slightly distally, 

 usually four to a pinnular. between the bases of which are the large and con- 

 spicuous sacculi. 



The tentacles contain numerous extremely slender spicules, which may form 

 a continuous layer along the outer side nearly or quite to the tip. 



Comatilia iridovietinformis (figs. 803-805, p. 378; see also figs. 763, 764, p. 

 353).— Large, conspicuous, and well-formed plates are present, five to each two 

 pinnulars. These are considerably higher than the lateral diameter of the pin- 



