380 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Protriaenes have a rhabdome about 5 mm. long, 12-18 \l thick 

 above, then tapering to a hair-like thickness; clads 60-80 [i long, 

 strong; cladomes projecting, or occasionally within the conulus but- 

 near the surface. 



Anatriaenes have a rhabdome which may reach a length of 10 mm., 

 8-15 [jl thick above, then hair-like; clads 40-60 jx long. These spicules, 

 very abundant in the bundle ; some cladomes projecting, but most in 

 the ectosome, those of younger spicules in the outer part of choano- 

 some. 



The specimen from D5141 is very different from the other two. 

 From the similarity in skeleton I conclude that it is probably a 

 young form of the same species. It is pyriform, 19 mm. high, with 

 a faintly papillose surface, the papillae supported by the radial bun- 

 dles. The upper rounded end appears to the eye to be without pro- 

 jecting spicules, the lower half showing such spicules, which how- 

 ever only protrude a short distance and do not form a root tuft. 



Brown granular cells are abundant in the ectosome, and the speci- 

 men differs from the preceding also in the following skeletal meas- 

 urements : 



The cortical zone of the ectosome is only 700 \). thick in the upper 

 part of the sponge, 1,100 jx thick below. The larger radial oxeas are 

 only about 2 mm. by 24 \l. The cortical oxeas are about 700 by 20 ^> 



The protriaenes are small; the rhabdome only 8-12 jjl thick, the 

 clads 40-60 [x long. These spicules barely project or do not project 

 in the upper half of the sponge. They are more abundant and they 

 project freely in the lower half. 



The anatriaenes are also smaller than in the other two specimens, 

 although they have the same shape and show the same abundance 

 and arrangement. The rhabdome is about 7 [x thick above, the clads 

 40 \l long. 



Genus PARATETILLA Dendy (1905). 



Paratetilla Dendy, 1005, p. 07. 



With a special layer of modified triaenes in the ectosome or at the 

 junction between ectosome and choanosome. The triaenes may de- 

 part from the ortho- or plagiotriaene type only in having a very 

 short rhabdome; or they may depart in various ways, becoming 

 irregular and lacking uniformity in one and the same sponge. Some 

 species with, some without, special poriferous depressions. 



PARATETILLA ARCIFERA. new species. 



Plate 40, fig. 2 ; plate 48, fig. 6. 



Station D5400, one specimen. 



Sponge subglobular. both upper and lower surfaces flattened. 

 Horizontal diameter about 30 mm. Shellv incrustations conceal a 



