OF CONCHOLOQY. ' 129 



probably from the circumstance that lower organisms offer fewer 

 specific characters. 



The marine animals are less influenced by the continents than 

 the terrestrial are. Thus the Atlantic coast of the old world 

 has nearly all the genera represented in closely allied species on 

 both sides of America. Many West Indinn species are exceed- 

 ingly difficult to distinguish from East Indian. The same rela- 

 tion is to be seen among species of the faunas of different geolo- 

 gical periods. Agassiz* has chiefly shown the relation of the 

 fossil forms to the living, and introduced a particular nomen- 

 clature. 



Prophetic types indicate the relations between Ichthyosaurusf 

 and Cetacea, or between Pterodactylus and Bats of the present 

 era; but this resemblance is scarcely anything but common 

 analogy, like the relation betAveen Tcstudo and Dasypus, &c. 

 This expression must therefore be understood in the manner 

 that the Ichthyosauri performed in the Liasic period the same 

 part in the house-keeping of nature as the Dolphins or Seals in 

 the present sea. 



Embryonic types (Ag.) indicate the relation betAveen Mastodon 

 and Elephant, Pentacrinus and Antedon, Sertularians and Me- 

 dusae. 



Hyp embryonic types (Ag.) indicate animals with embryonic 

 characters strongly developed, as the webbed hands of Bats and 

 Seals. 



XIV. According to the time in which animals seek their food, 

 are several very natural groups established, chiefly characterized 

 by the construction of the eyes and the colors of the body. 

 Ferse, Rapaces, Fissirostres, Lepidoptera are thus divided into 

 Diurnal, Crepuscular and Nocturnal. The latter division may 

 always be considered the lowest in rank. 



XV. The different means of protection against attack of 

 enemies or injuries from physical causes, offer often a good guide 

 to distinjiuish relative rank. 



1. Defensive arms, which are also used as offensive weapons : 

 teeth, claws, hoofs, horns, bills, poison-darts, cnidjB of Actiniae,! 

 pedicellaria of Echinodermata, avicularise of Bryozoa.§ 



* On the differeuce between Progressive, Enibryouic and Prophetic 

 Types.— Am. Ass. Adv. Sc. 1849. p 432. 



t As these animals have four limbs, the analogy is perhaps still closer 

 to the seals. 



X The cuidae, or urticating filaments of the EolidiB, appear to be 

 quasi-foecal collections of tlie thread cells of the Hydractinia) (Str. 

 Wright, Quar. Journ. of Microsc. Science, 1863, vol. 3, p. .52), reminding 

 one of the hair-balls of animals of prey, some Insectivora, as the Cuckoo. 



2 F. A. Smith, Ofversigt af Kgl. vel. Acad. FOrh., Stockholm, 1865. 



