Prof. W. Thomson on Iloltcnia. 285 



long. 7°20' W., about 20 miles beyond the lOO-fnthom line of the 

 Coast- Survey of Scotland, fine, grey, oozy mud, with forty or fifty 

 entire examples of several s])ecies of siliceous sponges. The mini- 

 mum temperature indicated by several registering thermometers was 

 47°''-i F., the surface-temperature for the several localities being 

 r)2°-o F. 



The mud brought up consisted chiefly of minute amorphous 

 particles of carbonate of lime, with a considerable proportion of living 

 Globiyerince Kndt. other Foraminifera, and of the " coccoliths" and 

 " coccospheres " so characteristic of the chalk-mud of the warmer 

 urea of the Atlantic. The sponges belonged to four genera : one 

 of these was the genus Ilyalonemu, previously represented by the 

 singular glass-rope sponges of Japan and the coast of Portugal ; and 

 the other three genera were new to science. One of these latter was 

 the subject of the paper. 



Associated with the sponges were representatives, usually of a 

 small size, of the ^loUusca, the Crustacea and Annelides, the Echino- 

 dcrmata, and the Ccclenterata, with numerous large and remarkable 

 rhizopods. Many of the higher invertebrates were brightly coloured 

 and had eyes. 



Four nearly perfect specimens of the sponge described in the 

 memoir were procured. 



HoLTENIA, n. g.* 

 II. Carpenteri, n. sp. 



The body of the sponge is nearly globular or oval. Normal and 

 apparently full-grown sjiecimens are from 9" to 1' I" in length, and 

 from 7" to 9" wide. The outer wall consists of an open, somewhat 

 irregular, but very elegant network, whose skeleton is made up of 

 large separate siliceous sj)icules. These spicules are formed on the 

 sexradiate stellate type ; but usually only five rays are developed, 

 the sixth ray being represented by a tubercle. To form the frame- 

 work of the external wall, the four secondary branches of the spicule 

 spread on one ])lane, the surface of the sponge, while the fifth or 

 azygous branch dips down into the sponge-substance. This arrange- 

 ment of the spicules gives the outer surface of the sponge a dis- 

 tinctly stellate appearance, the centres of the stars being the point 

 of radiation of the secondary branches of the spicules. These 

 quinqueradiate spicules measure about 1" 5'" from point to point 

 of the cross-like secondary branches ; and the length of the az\gous 

 arm is from 7'^'" to 1". 



Smaller stars, formed by the radiation of smaller spicules of the 

 same class, occuj)y the spaces between the rays of the larger stars. 



The rays of each star bend irreguLuly, and meet the rays of the 

 spicules forming the neighbouring stars. The rays of the different 

 spicules thus run along for some distance parallel to one another, 



* The genus is iiaiiiecl in eomjilimcnt to M. llulton, Governor of tlie Farof 

 Islands; and tlio species is detlicaled to Dr. \V. B. Carpenter, V.P.K.S., witli 

 whom the autlior was associated in llie conduct of the expedition. | A figure of 

 the .species is given at p. H'O of the presi-nt vohiinc of the 'Annals.'] 



Ann. d: Mcifj. X. Hist. Ser. 4. Vol. iv. 20 



