OCR Text |
Show 616 MR. W. S. KENT ON A N E W GENUS OF SPONGES. [June 20, Order SILICEA. Gen. nov. CAULOSPONGIA. Sponge consisting of a central stem or axis, around the distal portion of which the sponge-body is disposed in separate whorls, or in more or less regular or irregular spiral convolutions. Skeleton compound, consisting of a primary network of keratose fibre, with siliceous spicula irregularly imbedded in it, and an accessory one of siliceous spicula only. Spicula of one form, simple, spinulate, arcuate. 1. CAULOSPONGIA VERTICILLATA. (Plate XLVIII. fig. I.) Sponge-body forming interrupted ascending spiral, or regular and separate infundibular expansions. Central axis and stalk fistulose, the internal cavity frequently communicating with the exterior by means of exteusive oscula. Skeleton kerato-siliceous, consisting principally of horny reticulated fibre with siliceous spicula imbedded in it, but having an accessory and superficial one of spicula imbedded in sarcode only. Spicules spinulate, slightly arcuate; average length JJJ inch. Hab. North Australia. Free Public Museum, Liverpool. 2. CAULOSPONGIA PLICATA. (Plate XLVIII. fig. 2.) Sponge-body forming contorted laminate convolutions, having an irregular ascending spiral direction. Stalk fistulose above the commencement of the body, with numerous oscular passages, compact beneath. Skeleton kerato-siliceous as in the last species. Spicula spinulate, slightly arcuate ; average length ^ inch. Hab. Unrecorded. B.M., presented by Miss Saul. In the existence of a primary and secondary siliceo-fibrous skeleton, this new genus appears most closely to approach Diplodemia of Bowerbank, an incrusting form with simple acerate spicula, regarded by its author as forming a connecting link between the Keratose and Halichondraceous tribes of Sponges. In the drawing which I exhibit (Plate XLVIII.) fig. 1 represents Caulospongia verticillata reduced to one half its natural size, and fig. 2 the true proportions of C. plicata. The single specimen examined of the first of these exhibits a series of sliglitly prominent ridges radiating from the centre to the circumference of the infundibular or spirally ascending expansions of the sponge-body, these being most conspicuous on the upper surfaces. In both species the passages communicating with the internal cavity of the fistulose stem would appear to represent the only distinct oscular system. |