462 ON THE FAUNA AND BOTTOM-DEPOSITS NEAR THE 30-FM. LINE 



The presence of Astropectcn on the gravel and broken-shell grounds 

 around the Eddystone would appear to be a good illustration of the 

 way in which the fauna of a particular ground may be influenced by 

 the fauna of surrounding grounds {<■/. p. 388). It will be seen 

 from the chart that these gravels occupy a comparatively small area, 

 which is almost entirely surrounded by grounds on which the bottom- 

 deposit is composed of fine sand, which is the true home of the species. 

 The few specimens taken on the gravel would therefore appear to be 

 rather of the nature of immigrants from these surrounding grounds. 



The Polynoid Acholoe astericola is almost invariably found associated 

 with this species, living in its ambulacral groove. 



Habits. Astropecten irregularis is specially adapted both for pro- 

 gressing rapidly over the surface of the sand and for burrowing beneath 

 it. The conical pointed tube-feet are the organs by means of which 

 both these movements are accomplished. From observation of the 

 species in the aquarium it appears that a great part of its life is spent 

 beneath the surface of the sand. The process of burrowing, which is 

 executed by the rapid movement of the tube-feet, has the appearance 

 of a vertical sinking in the sand. The species remains at rest for long 

 periods, with the central portion of its disc raised in a tall conical 

 protuberance, the apex of which projects above the surface of the sand. 

 The formation of a similar protuberance was described by Cuenot (No. 

 17, p. 385, and No. 18, p. 55) in the two Mediterranean species, 

 Astropecten spinulosus and squamatns [ = A. jonstoni (Dolle Chiaje)]. 

 Sladen (No. 106) describes such prominences on the disc of several 

 species of Astropecten taken by the Challenger, and the same author has 

 described a similar but much more elongated and non-retractile promi- 

 nence as a family character of the Porcellanasteridae. 



The food of Astropecten irregularis, as of other species of the genus, 

 consists largely of bivalve and GasLeropod molluscs, but small Echiuo- 

 derms and Crustaceans are also eaten. I have myself found in the 

 stomach of one specimen (haul 104) Echinocyamus pusillus, a fragment 

 of Hippohjlc sp. (?), and Natica nitida. 



Forbcs (No. 22) states that he has found Venus cassina in the 

 stomach of this species, and that Ball found in one specimen nine 

 Natica Alderi and a Ihirritella terehra {=T. comiimnis). 



Distribution. Geotjraphical. A. irregularis has a iioitheni distribution. It occurs 

 off the coast of Norway, in the Kattegat, on all British Coasts, and off the west coast 

 of France (TiUdwig, No. 70, p. 15, note 1). It does not ocfur in the Jlediterrancaii, tlie 

 statements that it is found there made by several authors resting on a record of Marion's, 

 which Ludwig {I. c, p. 47 and p. 49, note) has shown to be based on a mistaken identifica- 

 tion of the species A. jjenlaccmthus, var. scrralus. Studer (No. 108) states that A. 

 irregularis was taken in the Gulf of Guinea in 59 fathoms. There is no other record, so 

 far as I am aware, which coufn-ms such a southerly extension of the species. 



Depth. The species has a very considerable range of depth. MObius and Biitschli (No. 



