Mr. S. O. Ridley on Sponges. 183 



sea-water is very different from that of ordinary caverns. 

 While it may be possible that this modification of the dark- 

 ness of the ocean abysses is due to phosphorescence of the 

 animals themselves, it does not seem probable that it is wholly 

 due to this cause. 



The large size of the eggs is a marked feature in many of 

 the deep-water Decapoda. The eggs of Eupagurus politus 

 from 50 to 500 fathoms are more than eight times the volume 

 of those of the closely allied and larger E. hernhardus from 

 shallow water ; and in Sahinea princepis^ from 400 to 900 

 fathoms, they are more than fifteen times as large as in >S'. 

 septemcarinata from 25 to 150 fathoms. The most remark- 

 able cases are among the deep-water genera. Galacmitha 

 rostrata and G. Bairdii^ from between 1000 and 1500 fathoms, 

 have eggs 3 millim. in diameter in alcoliolic specimens, while 

 in the vastly larger lobster they are less than 2 millim. The 

 largest Crustacean eggs known to me are those of Parapa- 

 siphae sulcatifrons ^ a slender shrimp less than 3 inches long, 

 taken between 1000 and 3000 fathoms. Alcoholic specimens 

 of these eggs are fully 4 by 5 millim. in shorter and longer 

 diameter, fully ten times the volume of the eggs of Pasiphae 

 tarda from 100 to 200 fathoms, more than 350 times the 

 volume of those of a much larger shallow-water Palcemon, 

 and each one more than a hundredth of the volume of the 

 largest individual of the species. From the peculiar environ- 

 ment of deep-water species it seems probable that many of 

 them pass through an abbreviated metamorphosis within the 

 egg, like many freshwater and terrestrial species, and these 

 large eggs are apparently adapted to produce young of large 

 size, in an advanced stage of development, and specially fitted 

 to live under conditions similar to those environing the adults. 



XXIV. — Notes on Sponges, toith Description of a new Species. 

 By Stuart O. Ridley, M.A., F.L.S., &c. 



The following remarks are either based on specimens recently 

 added to the collection in tlie British Museum, or suggested 

 by the study of the collection. 



MONACTINELLIDA. 

 Clialmidse. 



Cladochalina diffusa, n. sp. 



Cladochalina diffusa, Hidley, Report on the Zoological Collections made 

 during the Voyage of H.M.S. ' Alert,' p. 672, pi. xli, fig. 1), d, d'. 



Suberect, branching subdichotomously in one or more parallel 



