Mr. G. 13. Sowerby on Scissurella. Qo5 



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

 of them are sometimes split into two parts ; the base of tiie 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 hi/ 

 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 tliatof several of the Pleurotomae among 

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

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



♦ Translated from tlie first volume of the Memoires de la Sociele d'Histoirc 

 Nalurelle de Paris, p. 340. 



+ I have not tlious^ht 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 Pleurotoiflaria, 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 contimie to the ed>re of the shell ; 

 but as in Flaliotis and Fissurella (the only shells that possess the sliglmst ana- 

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

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

 cumstance it differs materially from Plcuroloinaria, it should coiislitute a new 

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

 assertion, is with the Fissurell.'u and Ilaliotides: 4thly, that it cannot therefore 

 belong to the family of Trochoida. Considering the great diversity of chnriitter 

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

 cies, and also considering that the shells in (|UC?lion are xicry minute, ihouuh we 



