DISTRIBUTION IN DEPTH. 439 



V. 



Date Nov. 25th, 1841. 



Locality S. extremity of Gulf of Maori. 



Depth 230 fathoms. 



Distance from shove One mile (shore steep). 



Ground ; . Fine yellowish mud. 



Number Number 



Species. of living' of dead Observatiot 



specimens, specimens. 



Terebratula vitrea 2' 



Synclosmya profundissima .... 3' 



Ai-ca imbricata 1 1' 



Dentalium quinquangulare.. ..I 



Hyalea gibbosa ; . 1 



Cleodora pyramid^ta 8 



Criseis spinifera 5 



The Distribution of the Mollmca in Depth has been investigated by 

 MM. AudouiQ and Milrle-Edwards, M. Sars, and Prof. E. Forbes. By these 

 observers the sea-bed is divided into four principal regions : — 



1. The Literal zone, or tract between tide marks. 



2. The Laminarian zone, from low-water to 15 fms. 



3. The Coralline zone, from 15 — 50 fms. 



4. The deep-sea coral zone, 50—100 fmS. or more. 



1. The Literal tore depends for its depth on the rise and fall of the tide, 

 and for its extent on the form of the shore. The shells of this zone are raoi e 

 limited in their range than those which are protected from the vicissitudes of 

 climate by living at some depth in the sea.* In Europe the characteristic 

 genera of rochj shores are Litorina, Patella and Purpura ; of sandy beaches, 

 Cardium, Tellina, Solew, gravelly shores, Mytilus ; and on muddy shores 

 Lutraria and Pidlastra. On rocky coasts are also found many species of 

 Haliotis, Siphondria, Fissvrella, and Trochus ; they occur at various levels, 

 feom'e only at the high-water line, others in a middle zone, or at the verge of 

 low-water. Cyprcea and Conus shelter under coral-blocks, and Uerithium, 

 Te.rehra, Natica, and Pyramidella bury in sand at low water, but may be 

 Ibund by tracing the marks of their long bui-rows. {Ifacgillivray). 



2. Laminarian zone. — In this region, when rocky, the tangle {Laminaria) 

 and other sea-weeds form miniature forests, the resort of the vegetable feed- 

 ing rnoWmV.^— Lacuna, Rissoa, Nacella, Trochus, Jphjsia, and various J\^«^/i- 

 braiichiata. On soft sea- beds bivalves abound and form the prey of Bucci- 



* Some of the litoi-al shells, like Purpura lapillus and Litorina rudis, have no free- 

 swimming larval condition, but Commence life as crawlers, with a well-developed 

 shell. Their habits are sluggish^ and their diffusion by ordinary means must be 

 exceedingly slow. 



