86 



MANUAL OF THE MOLLTTSCA. 



Modiola Carolineneis. 



„ plicatula. M. Y. 

 Pinna rnuricata. SC. 

 Area ponderosa. SC. 

 „ pexata. M.F. 

 „ incongnia. SC. 

 „ transversa. M. Y. 

 Solemya velum. M. Y. 



„ borealis. M. 

 Cardiuin ventricosum. SC. 



„ Mortoni. M. Y. 

 Liicina contracta. Y. 

 Astarte Mortoni. Y. 



,, bilunulata. F. 

 Cardita incrassata, F. 

 Venus mercenaria. M. SC. 

 „ Mortoni. SC. F. 

 „ gemma. M. Y. 

 Artemis discus. SC. 

 Petricola dactyltis. M. SC. 

 „ pholudiformis. Y. 



Mactra similis. SC. i\I. 



„ solidissinia. M. Y. 



„ lateralis. M. Y. 

 Lutiaria lineata. F. 



„ canaJioulata. Y. P. 

 Mesodesma arctata. M. Y. 

 Tellina tenta. M. SC. 



„ 8 sp. SC. F. 

 Semele aequalis. SC. 

 Ciimingiatellinoides. M. 

 Donax fossar. Y. 



„ variabilis. G. F. 

 Solecurtus fragilis, M. SC. 

 „ caribbaeus. M. F. 

 Corbula contracta. M. F. 

 Periploma Leana. M. Y. 



„ papyracea. M. Y. 

 Lyonsia liyalina. Y. 

 Pandora trilineata. M. F. 

 Pholas costata. SC. F. 



„ semiuostata. SC. 



LAND EEGIONS. 

 Distrihution of Land and Fi^esh-iuater Shells. 



The boundaries of the Natural-history land-regions are more 

 distinctly marked, and have been more fully investigated, than 

 their counterparts in the sea. Almost every large island has its 

 o-v\-n fauna and flora ; almost every river system its peculiar 

 fresh-water fish and shells ; and mountain-chains like the Andes 

 appear to present impassable barriers to the "nations" of 

 animals and plants of either side. Exceptions, however, occur 

 which show that beyond this first generalisation there exists a 

 higher law. The British Channel is not a barrier between two 

 provinces, nor is the Mediteri'anean ; and the desert of Sahara 

 separates only two portions of the same zoological region. In 

 these and other similar instances the " barrier" is of later date 

 than the surrounding fauna and flora. 



It has been often remarked that the northern part of the map 

 of the world j^resents the appearance of vastly-extended, conti- 

 nental plains, much of which is, geologically speaking, new 

 land. In the southern hemisphere the continents taper ofi" into 

 promontories and peninsulas, or have long since broken up into 

 islands. Connected with this is the remarkable fact that only 

 around the shores of the Arctic Sea are the same animals and 

 plants found through every meridian ; and that in passing south- 

 ward, along the three principal lines of land, specific identities 



