462 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Spicules. — 1. Skeletal desma, monocrepid; commonly rodlike 

 without clads and with two concave articular surfaces (pi. 50, fig. 

 13). Rod somewhat curved or bent: smooth or slightly roughened 

 with a few vague elevations: ends tapering, or rounded and blunt, 

 sometimes gnarled. Rarely desmas occur (pi. 50, fig. 8) in which 

 the epirhabd has developed one or a few clads, the articular facets 

 still remaining on the epirhabd. The desmas are loosely articulated 

 together and fall apart during boiling. They are distributed uni- 

 formly throughput the parenchyma. Common length of desma, 

 2.0-2.5 mm., diameter 110-170 p. ' 



2. Large oxeas (pi. 50, fig. 14 a), 2-2.5 mm. long, about 70 \l 

 thick; arranged more or less vertically to the dermal membrane 

 at both surfaces. 



3. Plagiotriaenes (pi. 50, fig. 11, &), abundant at both surfaces. 

 Rhabdome about 850 jjl long, 45 \i thick: clads 400 j/. long. Numerous 

 smaller sizes present. The spicules sometimes, rarely, assume par- 

 tially or completely the dichotriaene character in that one or more 

 rays fork. 



At the outer surface the spicules form an exposed crust or armor 

 outside the dermal membrane. In this extradermal crust the 

 cladomes are paratangential to the surface of the sponge, the rhab- 

 clomes radial, the spicules forming several layers. The spicules 

 evidently emerge from the sponge body at slight elevations of the 

 actual dermal surface; from such elevations numerous spicules may 

 be seen protruding, the rhabdomes diverging somewhat from one 

 another. Plagiotriaenes quite like the extradermal ones lie also in 

 the ectosome, the cladomes supporting the dermal membrane, the 

 rhabdomes radial. 



At the inner surface a thick extradermal crust of plagiotriaenes 

 is not present, although a considerable number of spicules project 

 through the dermal membrane, the cladomes becoming extradermal. 

 Cladomes of other spicules are in the ectosome and support the 

 dermal membrane, the rhabdomes radial. 



4. Small oxeas (pi. 51, fig. 1, a), so-called microxeas, very abundant 

 in the parenchyma: smooth and evenly tapering. 90-165 \i by 4 [x. 



5. Microrhabds (pi. 51, fig. 1. &), in the form of microstrongyles 

 about 20 by 5 pi, exceedingly abundant in the dermal membrane at 

 both surfaces. Outline of spicule irregular, the irregularities some- 

 times sufficiently pronounced to deserve the name of protuberances. 



G. Streptasters (pi. 51. tig. .1. c), with very short axis and rays 

 that are often vaguely grouped at the two ends of the spicule; 

 abundant in the parenchyma. Total length of spicule about 15 ja, 

 ray length 5-7 \j.. 



Holotype.—C&t. No. 2134:}, T'.S.X.M. 



