1874.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 301 



labelled " Mexico." It is firmly based on the remains of the stem 

 of a fueus. The surface, to the unassisted eye, has a minutely reti- 

 culated appearance, arising from the closely disposed and exceedingly 

 numerous porous depressions ; but in the living state it would most 

 probably be quite smooth. The oscula were congregated in an irre- 

 gular group near the basal attachment ; they are simple in structure 

 and very small, the largest of them scarcely a line in diameter. The 

 internal structure is remarkable for the abundant varieties of its 

 spicula. The skeleton-fasciculi are composed of numerous, somewhat 

 slender, fusiformi-acerate spicula ; and the fasciculi are very much 

 strengthened near the surface of the sponge by the incorporation in 

 their substance of the shafts of the numerous connecting spicula, 

 those of the patento-ternate ones frequently being nearly twice the 

 diameter of those of the skeleton and considerably longer ; both the 

 patento-ternate and the recurvo-ternate ones are numerous ; but the 

 porrecto-ternate forms are of rare occurrence and are frequently very 

 slender. The interstitial membranes are abundantly supplied with 

 the two forms of retentive spicula, and especially so with the smallest 

 of the two forms. A fully developed one, of the largest size, mea- 

 sured yyVo mcn extreme diameter ; and two of the smaller descrip- 

 tion were 3^-5- inch and 42 ^ 6 inch in diameter ; and the latter one 

 was not the smallest one in the field of view. The radii of the 

 largest form were always acutely terminated, while those of smaller 

 ones were truncated or slightly expanded at their distal termina- 

 tions. The retentive spicula are very characteristic of the species, 

 from their minuteness and great abundance on the interstitial 

 membranes ; while, on the contrary, the tension-spicula are com- 

 paratively of rare occurrence. 



The ovaria are abundantly dispersed on all parts of the interstitial 

 membranes in various stages of development. 



Halispongia ventriculoides, Bowerbank. (Plate XLVI1. 

 figs. 1 & 2.) 



Sponges from Otaheite, Ellis and Solander's Natural History of 

 Zoophytes, p. 206, tab. 59. figs. 1, 2, 3. 



Spongia otahitica, Esper, vol. ii. tab. of Sponges lxi. (copied 

 from Ellis and Solander). 



Sponge cup- or fan-shaped, thin ; pedicle short and stout. Surface 

 rather prominently ridged or mammillated in lines radiating from 

 the base to the distal margin, ridges or mammae more or less 

 elongated, margin of cup thick and rounded. Dennis retiform ; 

 rete abundantly arenulous. Oscula simple, minute, dispersed, few 

 in number. Pores inconspicuous. Skeleton — primary fibres abuu- 

 dantly arenulous ; secondary fibres rarely arenulous. 



Colour in the dried state ochreous yellow. 

 Hab. South Sea, Otaheite. 

 Examined in the dried state. 



The prevailing form of this species is the cup-shaped one, subject 

 to a cousiderable amount of variation. The specimen represented by 



