MILNE-EDWARDS. 593 



stellar constellations that crowd the glorious vault of heaven. 

 Guided hy these views, Milne-Edwards classifies the Gas- 

 teropods thus: 



Class GASTEROPODA. 



Cephalous Mollusca, with a fleshy foot for locomotion, 

 formed by a posterior lobe of the head ; the organs of gene- 

 ration unpaired and unsymmetrical, and the entire organ- 

 ism modelled on a spiral line, either in the larva state only 

 or throughout life. 



Typical Group, or Subclass I. NORMAL GASTERO- 

 PODS. 



Foot fleshy, flattened, and very large ; abdomen well de- 

 veloped, &c. 



1 Section. PULMONATED GASTEROPODS. 



Larva with a naked head, &c. ; vessels of the lesser circu- 

 lation reticulated ; androgynous. 



2 Section. BRANCHIFEROUS GASTEROPODS. 



Larva with cephalic swimmers, &c. ; vessels of the lesser 

 circulation fasciculated. 



Order I. OPISTOBRANCHIA. Cervical region naked, &c. 

 Order II. PROSOBRANCHIA. Cervical region surmounted 

 with a vaulted pallial cavity, &c. 



Aberrant Group, or Sub-class //.SWIMMING GAS- 

 TEROPODS, OR HETEROPODS. 



Foot fleshy, vertical ; abdomen rudimentary, &c. 



Satellitious group of GASTEROPODS pendulous from the 



Prosobranchia. 



Family, CHITONID^E. Cephalous Mollusca ? with a 

 fleshy foot ; the body subannular ; generative organs paired 

 and symmetrical : a medial dorsal vessel, &c.* 

 These great reforms of Milne-Edwards derive support 

 from the delicate and elaborate dissections of his young 

 friend, M. Emile Blanchard. This adroit and gifted natu- 

 ralist, in addition to the characters above assigned to the Opis- 

 tobranches, tells us that the cephalic ganglia of the nervous 

 system have a closer centralisation than they have in other 

 Gasteropods, a fact which had been previously made known 

 to us, in many Nudibranches, by Mr. Hancock and Dr. Emble- 



* Annales des Sciences Naturelles, ix. (1848), p. 102 112. It appears 

 the classification was first published in August, 1846. Mr. J. E. Gray has 

 defined the genera of Chitonidse in the Ann. and Mag. N. Hist. xx. 66. 



Q Q 



