BLAINVILLE. 547 



,, 10. Adesmacea. Gen. : Pholas, Teredina, 

 Teredo, Fistulana, Septaria. 

 ■ Order IV. HETEROBRANCHiATA=Acephales sans coquil- 

 les, Cuv. 



Family 1. Ascidiace a = Ascidia, Lin. 



Tribe 1. Simple Ascidia. Gen. : Ascidia, Bipapil- 



laria, Fodia. 

 Tribe 2. Compound Ascidia. — Gen. : Pyura, Dis- 

 toma, Botryllus, Synoicum. 

 ,, 2. Salpacea. 

 Tribe 1. Simple. Gen. : Salpa. 

 Tribe 2. Compound. Gen. : Pyrosoma. 



Sub-type. MALENTOZOARIA. 



This division embraces two very dictinct classes. The first 

 named Nematopoda is coequal with the genus Lepas of 

 Linnaeus, and the class Cirrhopodes of Cuvier ; and as they 

 are now considered to be constituents of the class Crustacea, 

 I pass over their arrangement. The second class is named 

 Polyplaxiphora, and is instituted for the sole reception of 

 the Chitons, multivalve shells with whose general appearance 

 you are now familiar. The class, according to De Blainville, 

 is very distinct from any other in the series of the animal 

 kingdom, and apparently is the medium of transition from 

 the cephalous mollusca to the Chetopodes, — an order in the 

 Entomozoa or annulose worms. This opinion is founded on 

 the kind of articulated shell which covers the back of the 

 Chiton, and on the circumstance that the vent is not lateral 

 and approximated to the mouth, as in other Mollusca, but 

 perforated at the opposite extremity to the mouth, and in 

 the median line, as it is in all Annelidans. 



Incapacitated by his blindness, Lamarck had called upon 

 M. Latreille to undertake his duty of delivering the lectures 

 on the history of avertebrated animals at the Jardin du 

 Roi ; and the result was a system of the Mollusca by this 

 great entomologist, in which the sexual peculiarities of the 

 class assume the first rank, as if Latreille had imbued him- 

 self with the fancies of Oken concerning the predominancy 

 of the sexual organs in the Mollusca. The system was pub- 

 lished in 1825, a little before the appearance of Blainville's 

 Manual, but subsequently to the publication of his classifi- 

 cation in the " Dictionnaire des Sciences Naturclles." The 

 following outline may give you some idea of it. Firstly 

 the invertebrate animals are divided into the Cephalidiens 

 and the Acephala. The Cephalidiens correspond to the 



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