ON ZGEAN INVERTEBRATA. 171 
Rissoa reticulata. |  Columbella rustica. 
Trochus exiguus. | Conus mediterraneus. 
Terebratula detruncata. 
When we inquire into the history of the species having such extensive 
ranges in depth, we find that more than one-half of them are such as have 
a wide geographic range, extending in almost every case to the British seas, 
and in some of those exhibiting the greatest range in depth, still further north ; 
many of them also ranging in the Atlantic far south of the gut of Gibraltar. 
If, again, we inquire into the species of Mollusca which are common to four 
out of the eight A2gean regions in depth, we find that there are 38 such, 2 
of which are either British or Biscayan, and 2 are doubtfully British, whilst 
of the remaining 15, 6 are distinctly represented by corresponding speoics in 
the north. Thus among the Testacea having the widest range in depth one 
third are Celtic or northern forms, whilst out of the remainder of Aigean Tes~ 
tacea, those ranging through less than four regions, only a little above a fifth 
are common to the British seas. One-half of the Celtic forms in the Hgean 
which are not common to four or more zones in depth, are found among the 
cosmopolitan Testacea, inhabiting the uppermost part of the littoral zone. 
From these facts we may fairly draw a general inference, that the extent of the 
range of a species in depth is correspondent with its geographical distribution. 
The proportion of Celtic forms in the faunz of the zones varies in the 
several great families of Testacea. In the accompanying tables I have exhibited 
this variation conchologically, in order that they may be more useful to the geo- 
logist than if the unpreservable species were included. It will be seen that 
there is a great disproportion in several of the regions between the number 
of Celtic forms of Univalves and of Bivalves, that whilst the Monomyaria 
and Dimyaria range as high as 35 and 30 per cent., the highest range of the 
Holostomatous univalve is only 13 and a fraction, and of the Siphonostoma- 
tous but 8, whilst the Aspiral species preserve a uniform per-centage of 6 in 
the three highest zones and of 3 in the three following. 
Conchological Table, No. I. 
Distribution of Shells in depth. 
ee nL) (Ga el eee 
Aigean 
Fatal Ill. | IV. | V. | VI. | VII. |VII. 
— 
= 
_ 


2 lesa 1/ 0 
G4yvGil ak 
Multivalves(molluscous)| 7| 3] 2) O|} 2 
Patelliform univalves ..| 20} 11/ 3] 2] 3] 5 
Tubular univalves (Den- 
Sere oe CNR 2) Sie 8 SGN ae EE aN 2a A” Ra 
Holostomatous spiral uni- 
valves (with Bulle and 
Auricula) .........-| 115 | 50 | 40 | 40 | 44 | 35 | 28 | 17 | 15 
Siphonostomat. and con- 
volute spiral univalves.| 104 | 40 | 27 | 30 | 41 | 36 | 30) 16 | 5 
Testaceous Pteropoda and 


Nucleobranchia...... 12 1 0; O Oo; 0} O 3 | 12 
Brachiopoda.......... Sel Oil a5 Ole las Aaah eas aati AW ie 
Conchifera Lamellibran- 
chiata........ ues 135 | 28 | 53 | 52 | 68 | 58 | 48 | 34 | 28 
408 |147 |129 |126 |142 |141 |119 | 85 | 66 
a 



