dredged up from the Gulf of Manaar. 369 



one. The spicules also of the specimens brought home bj 

 the Rev. A. E. Eaton from Kerguelen's Island^ and others 

 dredged up bj H.M.S. 'Porcupine' in the Atlantic Ocean, 

 are much larger than those of the common British species ; so 

 that this variation may extend even to our own shores, while 

 the single form, great variety in size, and long attenuation 

 towards the end of the spicule generally characterize the 

 species everywhere. 



Halichondria infrequens^ n. sp. 

 (PI. XVIII. fig. 9, a-d.) 



Of this sponge I can only record its spiculation, which 

 was found to the extent of half an inch on the surface of 

 Discodermia sinuosa (to be hereafter mentioned) , Spicules of 

 four forms, viz. : — 1, skeleton, acerate, curved, fusiform, 

 obtusely pointed at the ends, thickly microspined throughout 

 (fig. 9, a) ; 2, subskeleton (tibiella), cylindrical, straight or 

 undulatory, inflated at each end, smooth (fig. 9, h) ; 3, flesh- 

 spicule, bihamate, simple, contort, large (fig. 9, c) ; 4, flesh- 

 spicale, equianchorate, rather inclined to the " angulated " 

 (Bowerbank) kind (fig. 9, d). No. 1 forms the body struc- 

 ture ; and 2 is chiefly confined to the surface, where the flesh- 

 spicules are also most numerous. 



Hah. Marine. 



Loc. Gulf of Manaar. 



Ohs. The chief character here is the thickly microspined 

 acerate skeleton-spicule, which may perhaps be the represen- 

 tative of the spined acerate in Halichondria incrustans. 



The Tibiella. (PL XVIII. fig. 9, h.) 



From time to time, as it becomes evident that a certain 

 form of spicule is common to many sponges under various 

 modifications, it is desirable that a generic name should be 

 given to it, to avoid periphrasis in description ; and thus I 

 propose " tibiella " for that spicule so common among the 

 Fibulifera, Halichondrina, and some of the Suberitida, which 

 has a distant resemblance to the shin-bone, in which the shaft 

 may be straight or crooked, cylindrical or fusiform, long or 

 short, thick or thin, with the extremities simply pointed or 

 obtuse, or inflated and hastate, or inflated and clavate, spined 

 all over or only at the extreme end. Such are some of the 

 modifications which may be presented by Dr. Bowerbank's 

 "biclavated cylindrical" spicules ('British Spongiadse,' vol.i., 

 Terminology, p. 231, pi. i. fig. 19), and by "no. 2" in the 

 above description of Halichondr-ia infrequens (PI. XVIII. 

 fig. 9, h). 



