SPONGES COLLECTED IN PORTO RICO. 
385 
ing. The variations (many no doubt due to difference in the stage of development) in the size and 
shape of the megascleres, above indicated, may all be encountered in the same individual. 
In the center of the sponge, oxeas (4) are the only megascleres. Spicules (1), (2), (3), (4), all 
radiate outward from central portion as far as the cortex. Just within cortex the cladi of the ortho- 
trisenes may be arranged in conspicuous concentric layers, the larger spicules on the outside. In other 
specimens this concentric arrangement of the cladi is not conspicuous, the orthotrisenes of this region 
not being abundant, and nearly all comparatively small. From the interior separate spicules or 
bundles, containing each a few diverging spicules, radiate out through cortex to surface. Such spicules 
are large orthotrisenes (1), accompanied by anatrisenes (3), with occasional oxeas (4). Cladomes of 
the orthotrisenes lie just beneath the surface. Anatrisenes are frequently found projecting from surface. 
Microscleres. (6) Chiasters with a very small centrum or none, the rays very slender, minutely 
roughened, and somewhat tylote. Choanosomal chiasters have diameter 12 to Id ji and about 8 rays; 
somal, diameter 10 to 12 jt and about 12 rays. In some specimens the chiasters are rare throughout 
the sponge; in other specimens they may be abundant in the cortex and comparatively rare in the 
interior. 
Pilochrota fibrosa ( 0. Schmidt) Sollas var. gdobulariformis, n. var. 
Ancorina fibrosa, Schmidt, 1870, p. 67. 
Pilochrota fibrosa, Sollas, 1888, p. 180. 
Station 6079, one specimen. 
Schmidt (1. c. ) gave the name of Ancorina fibrosa to a sponge of irregular, incrusting habitus, with 
a clearly differentiated cortex. Schmidt says the megascleres are similar to those of A. simplimsima 
Schm. In this latter sponge (Schmidt, 1868, p. 18; Taf. in, fig. 9; Taf. iv, fig. 9) are found oxeas, 
anatrisenes (Anker “mit a b warts gekehrten Spitzen”), and plagiotrisenes. Sollas (1. c.) examined 
one of Schmidt’s preparations of this sponge and discovered chiasters, also determining size of oxea. 
He does not, however, in his diagnosis, mention the anatrisenes. 
The Porto Rico form, although differing in habitus from Schmidt’s specimen, agrees with it in 
the character of its spicules, and must therefore be identified as belonging to the same species. The 
specimen is spheroidal, 35 mm. in diameter, with one osculum, 4 mm. in diameter, leading into a 
cloaca-like cavity, into which efferent canals open. Surface uneven and almost completely covered with 
broken pieces of shell. Color, reddish-brown. 
Skeleton. — Megascleres. (1) Oxea 1.43 mm. by 0.027 mm., smooth, tapering to points. (2) Pla- 
giotrisenes very abundant; rhabdome about 1 mm. long, 24 // thick above, becoming very slender 
below, tapering to fine point; cladi 80 /u long, nearly straight, tapering gradually to a point. Ana- 
trisene not abundant; rhabdome about 1.45 mm. long, 16 ju thick above, becoming very slender below, 
tapering to fine point; cladi 52 ju long, sagitta 44 ju. 
Microscleres. (4) Chiasters are abundant and alike in ectosome and choanosome; total diameter 
12 ji) no differentiated centrum; rays tylote, 6 to 12. 
Genus TRIBRACHIUM Weltner (1882). 
Sponge produced into a special cloacal tube, the megascleres of which are orthodisenes. The 
characteristic microsclere is a sanidaster. 
Tribrachium schmidtii Weltner. 
Tribrachium schmidtii, Weltner, 1882. 
Tribrachium schmidtii, Sollas, 1888, p. 154, pi. xvn; pi. xli, fig. 5. 
Station 6067, four specimens. 
Sponge body is spheroidal, 5 to 8 mm. diameter; cloacal tube 3 to 5 mm. long. The Porto Rico 
specimens differ from the type as described by Sollas in the character of the somal trisenes. These in 
Sollas’ s description are orthotrisenes, but he mentions that “sometimes one or more cladi are bifur- 
cate” (1. c., p. 154) ; and in the explanation of fig. 17, pi. xvn, he mentions that dichotruenes occur near 
the base of the cloacal tube, but not elsewhere. In the Porto Rico specimens the somal trisenes are 
all dichotrisenes, but in view of the agreement in other respects with Sollas’s description, it does not 
seem advisable to make a new species on this evidently variable characteristic. 
