Prof. W. Thomson on Holtenia. 285 



long. 7° 20' W., about 20 miles beyond the 100-fathom line of the 

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

 entire examples of several species of siliceous sponges. The mini- 

 mum temperature indicated by several registering thermometers was 

 47°'3 F., the surface-temperature for the several localities being 

 52°-5 F. 



The mud brought up consisted chiefly of minute amorphous 

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

 Globifferince and other Foraminifera, and of the " coccoliths" and 

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

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

 of these was the genus Hyalonema, 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 MoUusca, the Crustacea and Annelides, the Echino- 

 dermata, and the Coelenterata, 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.* 

 H. Carpenteri, n. sp. 



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

 apparently full-grown specimens are from 9" to 1' 1" 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 spicules. 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 plane, the surface of the spbnge, 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 azygous 

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



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

 same class, occupy the spaces between the rays of the larger stars. 



The rays of each star bend irregularly, 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 named in compliment to M. Holten, Governor of the Faroe 

 Islands ; and the species is dedicated to Dr. W. B. Carpenter, V.P.K.S., with 

 whom the author was associated in the conduct of the expedition. [A figure of 

 the species is given at p. 120 of tlie present volume of the 'Annals.'] 



Aim. & Mag. N. Hist. Ser. 4. Vol'w. 20 



