358 MANUAL OF THE MOLLUSCA. 



cent, are common to Britain, and 137 range as far as the North coast of 

 Spain. 



The boreal shells of America are described by Dr. Gould.* From these 

 lists it appears that out of 140 sea-shells found on the coast of Massachusetts 

 north of Cape Cod, more than half are common to Northern Europe. 



Many of the species, it is believed, could only have extended their range 

 so distantly, by means of continuous lines of connecting coast, now no longer 

 in existence.f 



Boreal Shells common to Europe and North America. 

 * British species. 

 *Tereclo navalis. *Nucula tenuis. 



*Pholas crispata. *Mytilus edulis. 



*Soleu ensis. *i\Iodiola modiolus. 



* (Panopsea) Noi-vegica. *Crenella nigra. 

 *Mya areaaria. * „ discors, L. 



* „ trancata. * „ decussata, (glandula, Tot.) 

 *Thracia phaseolina (Conradi, Couth). Pecten Islandicus. 



Mactra ponderosa (ovalis, G.) ? Ostrea ednlis (borealis, Lam. ?) 



?Montacuta bidentata. *AnQmia ephippium. 



*Turtonia minuta. * „ aculeata. 

 ? Kellia rubra. ,, squamula ? 



? Lepton nitidum (fabagella, Conr. ?) ■ 



*Saxicava rugosa (arctica). *Terebratulina caput-serpentis. 



Tellina solidula, var. (fusca, Say). *EiiynclioneUa psittacea. 



* „ calcaria (sordida, Couth). 



*Lucina borealis. *Dendronotus ai-borescens. 



? „ divaricata. Polycera Lessonii ? 



*Cryptodon fl exuosus. ? Amphiagphyra hyalina (debilis ?) 

 *Astarte borealis. Cylichna alba (triticea, C.) 



* „ triangularis ? (quadrans, G.)j * „ obtusa (pertenuis). 

 *Cyprina Islandica. *Philine quadrata (formosa, St.) 

 ? (Cai-dium Islandicum, U. S.— N. Zemla.) 



Yoldia limatula. *Chiton cinereus. 



„ arctica, Gr. (=myalis). * „ marmoreus. 



*Leda pygmaea. * „ ruber. 



* „ caudata. * „ Isevis. 



? „ navicularis (lucida, Loven?) * „ asellus. 



* Report on the Invertebrata of Massachusetts. 1841. 



+ Forbes, Memoirs of the Geol. Survey, I. p. 379. Sir John Richardson, when 

 speaking of the cod-tribe and turbot-tribe, says : " Most of the fish of this order feed 

 on or near the bottom, and a very considerable number of the species are common to 

 both sides of the Atlantic, particularly in the higher latitudes where they abound. 

 It does not appear that their general diffusion ought to be attributed to migration from 

 their native haunts, but rather that in this respect they are analogous to the owls, 

 which, though mostly stationary birds, yet include a greater proportion of species 

 common to the old and new worlds than even the most migratory families. Several 

 of the Scomberoidece (Mackerel-tribe) which feed on the surface, have been previously 

 noted as traversing many degrees of longitude in the Atlantic : but the existence of 

 the ground-feeding Gadoidece in very distant localities must be attributed to a different 

 cause, as it is not probable that any of them wander out of soundings or ever approach 

 the mid-seas."— Report Zool. N. America, p. 218. 



