820 W. J. SOLLAS OX THE STRUCTURE .VXD 



one would apply very well to the other. Great interest attaches, 

 therefore, to Diseodermia as to the sole survivor of a once domi- 

 nant race; and this seems sufficient to justify us in giving a short 

 account of it. The figures 8 & 8« on PL XXVI., which have been 

 kindly furnished to me by Mr. Carter, illustrate the inner and outer 

 aspect of the single specimen of D. poly disc us preserved in the British 

 Museum. It came from the island of St. Vincent. "All the Lithis- 

 tina" Mr. Carter* remarks, " are short, sessile, or stipitate sponges 

 which grow on rocks or attached to stones ; " and this specimen is 

 " in general form shallow, cup-like, with an equally short, stout, 

 stipitate base. It is an inch in diameter and three quarters of an 

 inch high." Thus its outward form is generally similar to that of 

 some specimens of Siplionia ; and we must also observe that its 

 oscules are situate on the inside of the cup, just as they are in the 

 interior of the cloaca of the fossil genus. As regards the arrange- 

 ment of the canals in the recent specimen, we are without published 

 descriptions ; but Mr. Carter informs me that both they and the 

 skeletal network are arranged in most Lithistids in very much the 

 same fashion ; we may therefore supply this gap by an account 

 of what has been seen by Schmidt in a closely allied genus and 

 species, viz. Corallistes clavatella, Schmidt f. This sponge is also 

 stipitate : it is supported on a somewhat slender, not very short, 

 pedicel, which enlarges above into an expanded head, on the flat 

 superior surface of which the oscules are situated. Two sets of 

 canals are observed, the longitudinal or excurrent and the radiating 

 or incurrent ones, the latter reminding Schmidt of the canals and 

 furrows of Gnemidium, a fossil genus which appears to me to be 

 allied to Siplionia. Between the canals the spicules are arranged 

 with the " coarser, smoothest, and short arms lying concentrically," 

 and with their filigreed terminations lying in continuous bands 

 parallel with the radiate canals, the whole forming just such a 

 ladder-like arrangement as we have already found in Siplionia 

 (PL XXVI. fig. 1). 



This arrangement also, Mr. Carter informs me, is common to 

 most Lithistids ; and consequently our Siplionia resembles its exist- 

 ing allies not only in general form, but in the disposition of its 

 canals and principal spicules as well. 



To return to D. poly discus. "Its structure internally consists of 

 the filigreed spicules common to the Lithistidse (but of a peculiar 

 form, which will be mentioned directly), faced by a dermal layer of 

 thin, smooth, subcircular disks, with more or less curvilinear or 

 toothed margin, furnished respectively with a short, round, pointed 

 shaft, which projects internally, and imbedded in a dermal sarcode 

 densely charged with a minute, curved, acerate, microspined flesh- 

 spicule. The peculiarity of the staple spicule of the interior is that 

 it presents four smooth round arms, which, radiating irregularly from 

 a central point, soon divide into two branches respectively that termi- 



* Ann. & Mag. Nat. Hist. ser. 4, vol. xviii. pp. 460, 462. 

 t Grundziigo der Spcngienfaima des atlantischen Gobietes, p. 23, Taf. iii. 

 figs. 7, 7 a & b. 



