SILICIOUS AND HORNY SPONGES WILSON. 399 



membrane is perforated by uniformly distributed afferent apertures 

 1 mm. wide. Perhaps in his specimens the actual dermal membrane 

 had been torn off, thus leaving uncovered the apertures of the radial 

 afferent canals. Baer refers his sponge to R. implexa, but now that 

 another specimen has been taken from a different locality in the 

 east, the form may well be set apart from the type. 



The type was based (Schmidt, 1868, p. 27) on Adriatic specimens. 

 It was then recorded by Ridley and Dendy (1887, p. 15, pi. 1, fig. 4) 

 and by Topsent (1904, p. 244) from the Azores, by Dendy (1905, 

 p. 142) from Ceylon, and by Row (1911, p. 315) from the Red Sea. 

 The North Atlantic and Mediterranean sponges of the species have a 

 characteristic habitus (Ridley and Dendy, 1887, Topsent, 1904). The 

 sponge tubes are elongated, slender (about 7-10 mm. wide in the 

 Challenger specimen figured), and stipitate. Longitudinal poly- 

 spicular tracts probably always occur in addition to the renieroid 

 reticulum. In Mediterranean specimens examined by Ridley and 

 Dendy the oxeas measured 138 by 7 \l, in the North Atlantic speci- 

 mens the recorded range is from 160 by 6 [x (Ridley and Dendy) to 

 200 by 7-8 \i (Topsent). In Dendy's specimens from Ceylon the 

 tubes are only about 5 mm. in diameter, the multispicular fibers loose, 

 feeble, and sparsely present; oxeas 136 u, by 4 u,. Row's Red Sea 

 sponges resembled the Mediterranean forms. 



Genus PETROSIA Vosmaer (1887). 



Petrosia (Schmidtia Balsamo Crevelli) Vosmaer, 1887, p. 338. 

 Petrosia Ridley and Dendy, 1887, p. 9. — Topsent, 1894c, p. 4. — Lundbeck, 

 1902, p. 54. — Hentschel, 1912, p. 389 (some discussion of variation). 



Renierinae in which the skeleton consists of a reticulum of stout 

 polyspicular fibers or looser tracts, with very little or no spongin, 

 and often of scattered spicules besides. Spicules, oxeas or strongyles, 

 sometimes with intermediates. Consistency very hard, almost stony. 

 Some species approaching Paehychalina. 



PETROSIA TESTUDINARIA (Lamarck). 



Plate 40, fig. 6. 



Alcyonium testudinarium Lamarck, 1815, p. 167. 

 Reniera testudinaria Ridley, 1884, p. 409. 

 Petrosia testudinaria (Lamarck) Dendy, 1889, p. 77. 



Dendy, 1889 (p. 77), gives a detailed account of this species, based 

 on the study of a specimen from the Gulf of Manaar. This cup- 

 shaped sponge was 400 mm. high, 300 mm. wide at the base ; cavity 

 180 mm. deep, its aperture 380 by 170 mm. Outer surface with 

 prominent parallel ridges running vertically, ridges 40-50 mm. high 

 and about 50 mm. apart. Texture of dry sponge, fragile and crumb- 

 ling. Wide canals, at right angles to general surface, terminate on 



