with (lescriptions of new Species. 



347 



at various angles, and each tapers gradually to a fine point ; at 

 the place of junction there is generally a slight swelling. 



Several individuals of this species are buried in the specimen 

 oiTridacna gigas so often mentioned. In some of them the lobes 

 attain a great size, measuring half an inch in diameter. The walls 

 of the chambers are much more minutely punctured than in T. 

 cactoides ; and in one of the specimens examined the spicula differ 

 from those above described. In the specimen alluded to they are 

 multiradiate and triradiate of a peculiar character, the latter, 

 PI. XIII. fig. 8, having one of its rays cut short — little more 

 than a squarish tubercle indicating the point of union : the other 

 two rays bend from each other rather abruptly near the middle 

 and afterwards taper gradually to fine points. The multiradiate 

 spicula, PI. XII. fig. 11, are about three times the length of 

 the nodnlous bodies, and are rare and very complicated : they are 

 formed of two whorls of six or more rays each, the whorls being 

 jilaced rather near together on a central axis which is much pro- 

 duced at the ends ; the rays are straight, and, tapering gradually 

 to sharp points, have generally a rounded swelling near the ex- 

 tremity. 



I have not yet been able to determine whether the specimen 

 |)rovided with these curious spicula is distinct or not, though I 

 am inclined to believe that it is. 



EXPLANATION OF PLATES XH. XIIL XIV. and XV. 

 Plate XII. 



Fig. 1 . A portion of the surface of Cliona celata as seen in the compressor, 

 magnified about 400 diameters, exhibiting ci-ystalline bodies. 



— 2. Large ci-ystalline bodies from the same more highly magnified. 



— .'J. Small crystalline bodies also from the same, highly magnified. 



— 4. Chambers of C. lobata exposed by removing the surface of the ma- 



trix : — one half larger than nature : — a, papillary punctui'es. 



— b, 5. Portions of C. dendritica four or five times the size of nature, ex- 



hibited as seen through the transparent substance of the matrix. 



— 6, 6. Spicula of C. purpurea much enlarged : a, a spiculum still more 



highly magnified. 



— 7, 7. Spicula of C. rhovihea nuich enlarged. 



— 8. Ditto C. lobata ditto. 



— 9. Ditto C. millepunctata ditto. 



— 10. a, Crystalline nodulous bodies from the surface of Thoosa bulbosa; 



b, triradiate and quadriradiate spicula from the same, 



— 11. Multiradiate spicula from the surface of Thoosa bulbosal: a, an end 



view of a spiculum ; b, one of the rays more highly magnified. 



Plate XII I. 



F'l;/. 1. A portion of the branches and terminal twigs of Thoosa cactoides of 

 the natural size. 

 - 2. a, A portion of the surface of the same magnified about 200 diame- 

 ters, cxliibiting nodulous crystalline bodies; b, two of these l)odies 

 more hiohlv magnified. 



