SILICIOUS AND HORNY SPONGES WILSON. 291 



While in a specimen from D5218 the cladomes were'a little deeper 

 than hemispherical, with clads 120 \i long. 



3. Skeletal oxea, 2,000 by 21 [x and smaller. Together with the 

 shafts of the triaenes in the radial skeletal bundles, and strewn 

 irregularly in the central part of the sponge. 



4. Cloacal oxea, small and slender ; 250-340 by 5 \l. Tangentially 

 strewn in cloacal Avail; tangential in oscular membrane, radiating 

 toward osculum. In Sollas' specimens these spicules were 9 y. thick, 

 traversed the cloacal Avail radially, projecting and making the cloacal 

 wall hispid. In Lendenf eld's specimens (1906, p. 287) the spicules 

 are closer to mine in thickness, 180-250 by 4-6 y. ; probably radially 

 arranged, since there is no statement to the contrary. 



5. Chiasters, 8-12 \i in diameter, abundant at the surface and in 

 choanosome. In general smaller at the surface than in interior. 

 Rays long and slender, and distinctly tylote; rays 6-10 in number; 

 as usual, the fewer the rays, the larger the spicule. 



This agrees Avell with the records of Ridley (1884) and Sollas 

 (1888). Lendenf eld (1906, p. 287), however, finds that in his speci- 

 mens, when the chiasters are examined Avith an immersion objective, 

 they turn out to be " acanthtylasters " — that is, the rays, 3-12 in 

 number and cylindrical in shape, are armed at the end Avith a cluster 

 of spines and may be minutely spined along their course; total 

 diameter of spicule 6-16 [j., the size inA T ersely as the number of rays. 

 Sollas (1888, p. 119) had already found chiasters of this type in a 

 specimen which he described as M. toxodonta, and which Topsent 

 (1897, p. 433) merged in M. clavosa. Topsent 's synonymy has been 

 generally accepted. Lendenfeld assumes that the chiasters in the 

 species are ahvays " acanthtylasters," and hence that the A r ariability, 

 which is to be inferred from the records, is really due to the fact that 

 the spicules have usually not been examined with a high objective. 

 This conclusion, to be sure, remains to be tested. 



My own observations confirm Lendenfeld in the essential matter. 

 In tAvo specimens (from 1)5158) examined for this point, the enlarge- 

 ment, in which a ray terminates, was found not to be a ball but an 

 expansion subdivided into minute spines. This terminal expansion 

 seemed to be flattened, and the number of spines about 5; the ex- 

 pansion, when seen endwise, looking something like a little star. 

 The rays of the chiaster itself are approximately cylindrical, taper 

 a little toward the end, and arc in general without spines along their 

 course but now and then show one. 



MYRIASTRA SIEMENSI (Keller). 



Stelletta siemensi Keller, 1891, p. 341. — Lendenfeld, 1903, p. 36. 

 Station D5478, one specimen attached beloAv to a Euspoixjia ir- 

 regularis. 



