DREDGING ON THE COASiS OF SHETLAND. 329 



by Mr. Norman on the Echinodermata, by Mr. Peacb also on the last-named 

 class as well as the Poiyzoa, by Professor Allman on the Hydrozoa, by Mr. 

 Brady on the Foraminifera, and by Dr. Bowei'bank on the Sponges*. Buch 

 a division of labour has, I think, had the effect of increasing the result, and 

 making the whole more complete and valuable. 



I have been enabled by means of this expedition to confirm my former ob- 

 servations, embodied in the last Report, with respect to the nature of the 

 sea-bed which has been thus explored, and to certain physiological and 

 geological conditions. To these may be now added some further remarks. 



More quasi-fossil shells were dredged, and for the first time in this district 

 Lepeta cceca, dead, but apparently as fresh as any Scandinavian specimen. A 

 perfect specimen of Rhijmhonella psittacea was also obtained at a depth of 

 86 fathoms ; but it had two tell-tale associates. One was Pecten Mandicus, 

 and the other Spirorhis granulatus, var. heterostropha, of much larger size 

 than specimens of the same Annelid fi'om the southern coasts of England ; the 

 SpirorUs was also dead, and covered both the Rhijnchonella and Pecten. S. 

 granulatus has not been found in a living state north of the Hebrides, so 

 far as I have been able to discover. This appears to have been one of the 

 numerous relics of the glacial or post-glacial epoch ; it is an inhabitant of 

 shallow water, and affords another confirmatory proof of my hypothesis that 

 the Shetland sea-bed has sunk considerably during a comparatively recent 

 period. 



It seems to me as if shells belonging to the same species, that are common 

 to the littoral and deep-water zones, attain a greater size and thickness 

 in the former than in the latter habitat. Such are Venus gallina, Tellina 

 fabula, Mactra solkla (compared with its variety elliptka), Tectum virginea, 

 Rissoa Alderi {E. soluta of Eorbes and Hauley, but not of Philippi), Trochus 

 zizyphinus, T.cinerarms, T. tumulus, and Buccinum undatum compared with its 

 variety Zetlandka. Mr. Jordan informs me that he has observed the same 

 difference with regard to specimens of Pandora incequivalvis and its variety 

 obtusa, Tectura virginea, and Chiton discrepans, which he has lately taken on 

 the shore and dredged off the Channel Isles. More extensive observations 

 are unquestionably desirable, if not necessary, before this proposition can bo 

 substantiated; but it has been abundantly proved by the researches of Di. 

 Davy, Porchhammer, and Bischof that the quantity of carbonate of lime held 

 in solution by sea-water, and from which shells are secreted, occui-s chiefly 

 along coast-lines, being derived from terrestrial sources, and brought down 

 to the sea by rivers, streams, and the washings of rain and waves. This 

 would give a reason for littoral shells being more solid than those from deep 

 water; and possibly the greater abundance of food in the former than in the 

 latter case might account for the increase of bulk. 



I noticed in the last Eeport that living Mollusca taken by the dredge 

 from considerable depths, and placed in a shallow vessel of water di-awn from 

 the shore, did not appear to be in the slightest degTee affected by the sudden 

 change of bathymetrical conditions. I wish to qualify this statement, and 

 at the same time to record a further observation. It is quite true that the 

 Mollusca in question were lively and active in their new habitat ; but those 

 which were of the univalve kind exhibited a peculiarity and habits with 

 which I was much struck. All of them, on being placed in the vessel, tried 

 to escape from the bottom, and quickly found their way up the sides to the 

 open air ; some floated with the sole of the foot uppermost, and the shell 

 downwards. Now it is very certain that in their native habitat, at a depth 



-in/,. * ^^^^ ^^^ ^^ ^^ g'^^Ji in tlie next volume of Eeports. 



1864, '■ 2 



