68 PROCEEDINGS OF SOCIETIES. 



Before leaving the subject of dredging, I would wish to record the following 

 note from Captain M'Clintock, in reference to the naturalist's dredge: 



41 MY DEAR DR. BALL Although we have left our ships and almost all our 

 private property, as well as that belonging to the crown, behind us, yet the very 

 small collection my other duties permitted me to collect with the dredge, I have 

 brought home for you. There may be something of interest ; and, according to Sir 

 Edward Belcher, we have obtained some rare and new creatures. 



" Although Sir Edward has devoted so many years of his life mainly to shell 

 collecting, he was much struck with your little dredge ; he immediately borrowed 

 it, and had a larger one made of the same pattern. He confesses (and it is a great 

 confession for him) that it is the best he has ever seen. 

 " Yours, very sincerely. 



" F. L. M'CLINTOCK." 



The Genera Lacuna (except one species), Calyptrcea aplysia, Scrobicularia, and 

 Donax do not range in our seas below this, the Laminarian belt, and JRzssoa, 

 Chiton, Sulla, Trochus, Mactra, Venus, and Cardium have the majority of their spe- 

 cies within its precincts. 



A third region is the MEDIAN or CORALLINE ZONE, occupying the space been fifteen 

 and fifty fathoms. In its upper portion, Trochus ziziphinus and tumidus, Chiton 

 asellus, Acinsea virginea, Turritella communis, Venus ovata, and V. fasciata, 

 Pecten opercularis, Modiola modiolus, the common form of Crenella, Pectunculus 

 glycimeris, and Nucula nucleus, are characteristic testacea ; and on its lower half, 

 Solen pellucidus, Pecten varius, Dentalium, and Mactra elliptica. It is 

 marked more by the peculiarities of its species than by the exclusive presence of 

 genera. 



The fourth region is the INFRA MEDIAN ; its most characteristic portions are in the 

 extreme north. There are very few species of mollusca peculiar to it in our seas ; 

 those that are found are, for the most part, of rather small dimensions, and 

 remarkable for being of dull or pale colouring. Beneath this zone is the Abryssal 

 region, which cannot be said to be developed within the British seas. 



Besides these several subdivisions of the floor of the ocean, there are the high 

 levels of the sea- water itself, inhabited by a small assemblage of mollusks. The 

 Genera lanthina and Spirialis among our testacea, and our solitary species of 

 Salpa, as well as the curious and anomalous Appendicularia among Tunicata, are 

 inhabitants of this marine atmosphere ; all these forms are, however, very local 

 around our coasts. Bivalve mollusca would appear to be more extensively distri- 

 buted in depth and to constitute more constant links between zone and zone than 

 univalves. 



Having thus given some idea where the student will be likely to find the several 

 genera and species of marine testacea, we must turn our attention to the 

 Nudibranchs, or naked mollusca. These can be dismissed in a very few words ; 

 they are chiefly to be found in rocky places, which, indeed, is the favourite locality 

 for the majority of the Gasteropoda, and will be discovered creeping in the rock- 

 pools, or upon the fronds of algae. Next in order we come to land shells, and 

 there is not a place throughout the length and breadth of our country that some 

 one species may not be found. The common Helix aspersa is a follower of cultiva- 

 tion ; and where is the garden that cannot boast of the garden snail ? Some of them 

 prefer the sea-side, as Helix pisana, H. virgata, H. ericetorum, H. nemoralis, 

 Bulimus acutus, and others ; some keep themselves strictly secluded to the chalk 

 regions, as H. pomatia, H. carthusiana, Pupa secale, &c. ; some hide themselves 

 beneath moss, and it requires diligent search to find them, as H. pulchella, many of the 

 Pupa and Zonites ; others, again, climb to the tops of mountains, or love the retired 

 recesses of deep woods, as Helix arbustorum ; endless are the situations in which we 

 find the land shells, and few, if any, districts are without their fair proportion of them. 



The fresh-water shells are also found very widely distributed. In the swift- 

 running streams Cyclas cornea will be found, with others of the same genus, and 

 Ancylus fluviatilus holds hard to some large stone, braving most boldly the vigour 

 of the stream. In ponds of stagnant water, Limneus palustris, truncatulus, Bithinia 

 tentaculata, Planorbis corneus, and others will be found ; while, again, up in a 



