320 PROF. P. M. DUNCAN ON A 



thing more than doubtful. The absence of such an anal plate 

 in the ancient Cidarida?, the mode by which the anal plates 

 appear in Echinocidaris, the membranous condition which 

 obtains in Diadema (a form ancient enough, as we now know, 

 to retain a rudimentary internal gill), suggest that what is 

 seen in the more highly differentiated. Temnopleuridse is due to 

 some secondary process now considerably obscured. It is possible 

 that an increase in the rapidity of the rate of development has 

 here, as sometimes happens with the blastopore and the mouth 

 or anus, given to a more lately acquired structure a superficial 

 resemblance to one which was not even its proper predecessor. 



On a Lithistid Sponge and on a Form of Aphrocallistes from 

 the Deep Sea oft' the Coast of Spain. By Prof. P. Martin 

 Duncan, M.B. Lond., E.K.S., E.L.S., &c. 



[Bead February 17, 1881.] 

 (Plates XXIV. & XXV.) 



During one of the dredgings of the Expedition of H.M.S. ' Por- 

 cupine,' in 1095 fathoms, off the south-west coast of Spain, a mass 

 of fistulose coral was brought up ; it included, in its branches 

 many foreign substances, and. amongst them two small siliceous 

 sponges. The coral was described by me in my monograph of 

 the deep-sea corals # ; and lately my attention has been drawn to 

 the beautiful sponges. 



One of them, about an inch in height and one third of an inch 

 in thickness, has numerous oscules on it, and it is perfect in its 

 hard parts. Of the soft tissues no idea can be obtained. The 

 sponge evidently belongs to the Lithistidse ; for the skeletal 

 elements branch after the fashion of the group, interlock at their 

 ends with more or less filigreed terminations, producing a conti- 

 nuous network, and there are connective peltate spicula on the 

 outside. 



The sponge-body is very hard and resisting ; but it is smooth 

 to the touch and eye, and is of a dirty white colour ; the outside 

 of the body is faintly wrinkled here and there, and is produced on 

 the flanks and at the apex into several wart-like elevations, each 

 terminating in an oscule which leads deeply into the mass. The 

 oscular processes are short, unequal, differently directed, and 



* Trans. Zool. Soc. vol. viii. pt. v. p. 327. 



