REVIEWS. 43 



TOoment recollect whether the name Isthmia was first given to a 

 genus of Diatomacese or to the section of Pulmonifera to which our 

 author applies it, but most clearly it cannot stand in both situations, 

 and we believe the Diatomaceous genus is the one to be received. 

 The work before us is too much occupied with specific details to 

 afford matter for quotation, but the following passage will interest aU 

 who are engaged in studying Pulraoniferous Mollusca, and will give 

 a good idea of the author's mode of viewing the subject : 



" In the Helicidse, (as restricted here to those animals which sustain 

 a globose or planospiral shell) we have noticed thus far three principal 

 types of lingual dentition. 



"(1.) In those larger forms of Helices which we include under the 

 sub-family Helicinse, we have in the lingual membrane about one 

 hundred rows of plates, with about seventy-five plates in a row. The 

 laterals and uncini are scarcely distinguishable one from the other ; in 

 fact they may be said to blend together. The centrals and laterals 

 are unidentate and similar in form ; the uncini either unidentate, 

 bidentate, or irregularly notched. The buccal plate is solid, arcuate, 

 its frontal portion strongly marked with longitudinal ribs which 

 crenulate the cutting edge. 



" (2.) In another group which we designate as Helicellinse, we have 

 the viscera protected by a thin, glabrous shell ; the lingual membrane 

 is nearly as broad as long, having about sixty-eight rows of plates, 

 averaging about forty-two plates in a row ; the laterals and uncini are 

 quite distinct ; the central plate broad, long, tridentate ; the laterals, 

 three to five, bidentate, identical with central, in form of denticles ; 

 the uncini unidentate, the denticle being aculeate and re-curved. The 

 buccal plate is thin and crescent shaped, with a middle beak-like pro- 

 jection, lateral terminations pointed. 



" (3.) In a still smaller group, for which we propose the sub-family 

 name of Valloninse, we have the lingual membrane composed of eighty 

 or ninety rows or plates, averaging twenty-six plates in a row. The 

 laterals and uncini are generally distinct. The central plate is square, 

 tridentate ; the laterals four to five, square, bidentate ; uncini broad* 

 ehort, and minutely serrated. The buccal plate is slightly arcuate, 

 rarely produced centrally ; its front surface marked with delicate per- 

 pendicular or diverging striae, faintly notching the cutting edge ; the 

 lateral terminations of plate being rounded or blunt. 



" These three types of lingual dentition are accompanied with like 



