OCR Text |
Show 1881.] THE SURVEY OF H.M.S. c ALERT.' 127 as well as relatively stouter than in our Sponge. Outward form branching and fan-shaped. Its primary-skeleton fibres are far nearer together than here ; in composition they are 1- to 2-spicular in some parts, 2- to 3-spicular in others, while 2 to 3, occasionally 4, is the proportion in the present species. The proportion of horny matter in the fibre is generally, as here, only just sufficient to bind the spicules into a pliable fibre. The chief differences are shown in tabular form :- Composition of primary fibre ... ,, „ secondary fibre- Average maximum distance be- Chalinida granti, Bowerbank. (S. of England.) •133 m m . by •01056 m m. 1 to 3 spicules broad. 1 spicule broad. •142 m m . Of irregularly shaped anastomosing branches, subsessile. Rcnicra fortior, Schmidt. (Antilles.) •13788 m m . long. Amorphous. Reniera fortior, Schmidt. (Magellan.) •13935 m m . by •0094 m m . 2 to 3 (occasionally 4) spicules broad. 1 to 2 spicules broad. •284 m m. Erect, subglobose. R. fortior is only known to m e by its description, as the Museum possesses no specimen of it. SCHMIDTIA AULOPORA, Schmidt, var. Schmidtia aulopor a, Schmidt, Spong. atl. Geb. p. 44, pi. v. fig. 8. Thalysias sub triangular is, Duchassaing de Fontbressin et Michelotti ?, Spong. mer Caraib. p. 85, pi. i. fig. C , pi. xviii. fig. 1. Isodictya mirabilis, Bowerbank?, P. Z. S. 1873, p. 319, pi. xxviii. External Characters. A single fistula, about 40 millims. long and 19 broad at the broken base, and 12 broad at the vent-opening. It has evidently been torn off from a larger specimen, as the oblique fracture of the base of the tube shows. The walls are thickest at the base, viz. about 7 millims., and taper gradually up to the edge of the mouth, where they are of the thickness of cardboard. The whole tube tapers in breadth from base to mouth; but the internal diameter remains the same throughout. It presents a slight constriction or neck about 7 millims. below the mouth, below which point it has obscure longitudinal ridges, which become more marked as they approach the base, and are there accompanied by slight papillary eminences. Besides the large mouth or vent, tbjere is a lateral opening, about 3 millims. in diameter, leading upwards into the cavity of the tube. The colour is a dark brown throughout. The surface is regularly covered with minute points, between which lie the pores. Texture subelastic; the interior of tube has a honeycombed |