4d 



ACEPHALA LAMELLI- 

 BEANCHIATA. 



Poromya granulata 

 Lj'onsia Norvegica 

 Telliua donacina 



Lucina 



Pecten siaiilis 



„ polymoi-phus 

 Anomia ej^hippium 



Pteropoda. 

 Hyalcea tridentata 



Gasteropoda proso- 

 beanchiata. 



Chiton ? 



Patella tenuis 

 Emavfrinula 



Eissoa • 



Turritella? (Aclis?) • 



Mesalia striata 

 Scalaria Turtonis 



Murex erinaceus 

 Mangelia variegata 

 „ seealina 



Ampliispii-a hyalina 



Bifrontia Zancla?a 

 Jantliina pallida 



Consequently the Madeira species common to the Canaries are- 



Acephala lameUibranchiata A6 in 54, or 85 per cent. 



Acephala palliobranchiata 1 



Pteropoda 3 



Gasteropoda prosobrancliiata ... 73 

 Gasteropoda opisthobranchiata... (i 



Total, 129 in 156, or 83 per cent. 



From the foregoing statements it will appear that several species an(l 

 fonns typical of the Arctic fauna range far to the southward, whil 

 scarcety one of those characteristic of warm latitudes extends into hig! 

 northern regions. This would appear in a still greater degree, were thi 

 more southern districts as thoroughly explored as have been the coasts 

 of Britain, and the fact that such has not been the case should always 

 be borne in mind when drawing a comparison between the Mollusca of 

 Britain and of foreign countries. It will also be seen tliat the Acephala, 

 animals gifted with smaller power of locomotion, are more widely dis- 

 tributed than the Gasteropoda. 



I now proceed to give the result of my observations regarding the 

 particular points at which certain species and forms reach the extreme 

 limit of their range, northward or southward. 



Although, as already remarked, the transition from one fauna to 

 another is effected gradually, yet there are certain geographical points 

 at which a considerable change is observed to take place. The follow- 

 ing northern species reach their most southern habitat about 

 the northern and central parts of the British seas, though a few 

 of them rc-appoar on the Nymph Imnk, a kind of Arctic outpost oif the 

 south of Ireland. 



Punopoea Norvugica, North Sua 



Tellina proxinia, ,, 



Astarto elliptica, Cly(l(! and Nortli Sua 



„ arclica, Zetland 

 Cardinm Suecicum, Tnsh Sea 

 a 



CroncUa nigra. North Sea, Hebrides 



,, decussata, „ ,, 



Nucula tenuis, Scotland, Irish Sea 

 Leda pygnuna, Hebrides 

 Pecten nivens, ,, 



