Miscellaneous. 171 



prevalence of transformations throughout the Decapoda is not in- 

 dicated, the only reference to the larval forms being under the 

 head of Brachyura, and calculated to lead the student to the sup- 

 position that a metamorphosis is peculiar to that group of Decapods. 

 Under the Myriopoda Sir John Lubbock's curious genus Pauropus 

 ought to have received some notice. These arc small matters ; and 

 we must congratulate the author on having so well accomplished his 

 task. 



Of the ' Advanced Text-Book,' we need only say that it is an 

 abridgment of the Student's ^Manual, and follows the same general 

 course of treatment and classification. It seems to us well suited 

 for school purposes. 



MISCELLANEOrS. 



On the Assumption of the Adah Form by the Genera Cyprsea and 

 Ringicula, and by certain Species of the Genus Astarte. 



To the Editors of the Amials and Magazine of Natural History. 



Gextleiten-, — In the ' Eocene Bivalves,' just issued by the Palaeonto- 

 graphical Society, several species of Astarte are described ; and I 

 have there stated my belief that some species of this genus have the 

 peculiar character of producing an alteration in the ventral margin 

 of the adult shell, the young and growing animal having this part 

 always smooth, but that when full-grown it adds a row of denticu- 

 lations to the inside of the ventral magin ; and I called attention to 

 the peculiarities of the genus Cyprcea as throwing light upon the 

 subject. It has always been said that the young of the Cyprcece 

 have invariably the outer lip sharp and plain, with a visible spire, 

 but that, when full-grown, the animal contracts the aperture, in- 

 flects the outer lip, forms a row of denticles on each side of the 

 opening, and covers over the spire ; and when we find a shell in this 

 last condition, we have supposed it to be an animal that has attained 

 to its full proportions. 



In the Red Crag the species Trivia (Ci/prcea) europcea has been 

 found in great abundance ; specimens have been obtained from that 

 formation by hundreds ; and it is by no means rare in the Coralline 

 Crag ; but in all my search in these deposits, I have never seen one 

 of these shells that was in any other condition than that which is 

 assumed by the full-grown indi%'idual. The specimens of this spe- 

 cies in my o-\vn cabinet vary in size from g to nearly ^ of an inch in 

 length. 



There is another shell exceedingly abundant in the Coralline Crag, 

 viz. Ringicida buccinea ; and I have between three and four hundred 

 specimens before me, every one of which has a thickened margin to 

 the outer lip, and is presumably a full-grown shell. Now, although 

 I have closely examined these, and many others of the same species, 

 and have for years sifted great quantities of Crag, I have never seen 

 one that had not a thickened margin to the oiiter lip (with the ex- 



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