1873.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 5 



The lavgest description of stellate retentive spicula vary greatly in 

 their size and degree of development, and also in the number of their 

 radii. In some there are little or no indications of a spherical cen- 

 tral mass, and the number of radii does not exceed six or eight, while 

 others have well-developed central spheres and very numerous radii. 



The small stellate retentive spicula are very much more numerous 

 than the larger ones, and they all appear to have well-developed 

 spherical centres. The extreme diameter of an average-sized one 

 measured y- J^ inch ; and a smaller one did not exceed xthTTT inch. 

 The average greatest diameter of the larger description of stellate 

 retentive spicula was j^Vo i ncn - 



The ovaria do not exhibit any important specific characters. 



I have dedicated this species in memory of the veteran naturalist 

 the late Dr. Fleming, who has worked so much and so ably to extend 

 our knowledge of British natural history, and to whom we are indebted 

 for the first detailed description of a British Geodia, under the title 

 of Cydonium Miilleri, in his 'History of British Animals,' p. 515. 



Geodia depressa, Bowerbank. (Plate I.) 



Sponge massive, sessile ; surface minutely hispid, even. Oscula 

 congregated in depressed areas, numerous, small. Pores inconspicu- 

 ous, congregated 1 Skeleton-fasciculi large ; spicula fusiformi-acerate, 

 large and long. Connecting spicula attenuato-patento-ternate, large 

 and long, and recurvo-ternate, radii stout, shafts long and slender. 

 Interstitial membranes abundantly spiculous ; retentive spicula 

 attenuato-stellate, large and very numerous, and cylindro-sphero-stel- 

 late, small and very numerous. Ovaria spherical, slightly depressed. 



Colour in the dried state cream-white. 



Had. Dardanelles (J. T. Streatfield, Esq.), Museum of Royal 

 College of Surgeons, b. 181. 

 Examined in the dried state. 



This sponge is in size and form very like an irregularly compressed 

 Normandy pippin, its largest diameter being two and three quarters, 

 and its greatest height an inch and three quarters. Its original attach- 

 ment is at the thinnest part of its circumference, where there is a 

 small univalve shell about a quarter of an inch in length imbedded, 

 with a portion of a bivalve, apparently a Myl'dus, attached to it ; but 

 other than these substances there are no appearances of attachment, 

 and it had probably been freely floating about in the sea for a con- 

 siderable period before it was taken. On that which is apparently 

 its upperside, closely adjoining the shells above named, there is an 

 irregularly oval depression an inch and half in length and about a 

 quarter of an inch deep, in which the numerous small oscula are con- 

 gregated, and surrounding which there is a thick crop of large and 

 long fusiformi-acerate external defensive spicula ; and the remains of 

 similar spicula may be detected on other parts ot its surface. Beside 

 these large spicula, there is a secondary set of external defensive 

 ones, which are very long and slender, projecting through the der- 

 mal surface for about one-third or one-fourth of their length, and 



