Mr. G. 13. Sowerby on Scissurella. 255 



times very closely connected at their base, and indeed one or both 

 of them are sometimes split into two parts ; the base of the tube at 

 length becomes closed by the deposition of shelly matter on the 

 inside, and thus they do not become inbedded : I may conclude 

 therefore that this shell does not exhibit any anomalous formation, 

 but is constructed on the same general rules as all other shells are. 



Art. XXXVI. Abstract of a Monograph on a new Genus 

 of Gasteropodous Mollusca, named Scissurella. By M. 

 Alcide Dessalines D'Orbigny;* with Notes by 

 G. B. Sowerby, F.L.S. 



In prosecuting my researches among the marine and fossil sands 

 of various countries, in order to study the microscopic Cephalopoda 

 which are found in them, I have discovered the elegant minute 

 shells described in this memoir. The slit by which they are cha- 

 racterized is analagous to that of several of the Pleurotomas among 

 the Muricidae ; to that of the Emarginulae among the Scutibran- 

 chia ; and to that of the Siliquaria among the Annelidae :+ in fact 



* Translated from the first yolume .of the Memoires de la Societe d'Histoire 

 Naturelle de Paris, p. 340. 



+ I have not thought it necessary to translate the note extracted from the 

 report of Messrs. Prevost, Desnoyers, and De Ferussac, in which they endeavour 

 to show that the Genus now denominated Scissurella by D'Orbigny, has been 

 formerly published under the name of Pleurptomaria, given to it by De France, 

 and adopted by De Ferussac, because I am of opinion that those Naturalists, as 

 well as M. D'Orbigny are really mistaken : the following are my reasons : 1st, 

 that in all the specimens but one, of D'Orbigny's genus, that I have seen, 

 amounting to about a dozen, the slit does not continue to the edge of the shell; 

 but as in Haliotis and Fissurella (the only shells that possess the slighter ana- 

 logy) it forms a more or less elongated perforation, in the upper part of the last 

 volution, while the continvation of the lip is entire : 2ndly, that as in this cir- 

 cumstance it differs materially from Pleurotomaria, it should constitute a new 

 Genus: 3dly, that consequently its nearest analogy, contrary to M. D'Orbigny's 

 assertion, is with the Fissurellaa and Haliotides : 4thly, that it cannot therefore 

 belong to the family of Trochoids:. Considering the great diversity of character 

 that exists between the very young and the full grown shells of the same spe- 

 cies, and also considering that the shells in question are very minute, though we 



