74 BihliograpJiical Xotices. 



imperfect, and suggestions may be made for improvement in the 

 details, the eminent scientists have done good in opening up a vast 

 field of research for conchologists. Dr. Noetling gives his reasons 

 for preferring Prof. Bernard's system, and adopts it with some minor 

 alterations. The following statements are nearly all in the author's 

 own words. 



The teeth have been evolved from primary lamellae (that is, simple 

 ridges) on the anterior and posterior side of the cardinal margin. 

 The posterior primar}' lamellae remained simple throughout the 

 whole life, and no case is known in which secondary teeth originated 

 from them ; but whether originally or only subseciuently, they are 

 always anteriorly inclined (prosoclino). The anterior primary 

 lamella% however, indicate various changes at their posterior end by 

 thickening and curving, which eventually resulted in the differen- 

 tiation of the cardinal teeth. In the differentiated primary lamellae 

 the anterior laterals are always, and the anterior cardinals mostly, 

 posteriorly inclined (opisthocline), while the posterior cardinals are 

 always prosoclins. 



It is supposed that the anterior cardinal tooth was formed at the 

 posterior end of the primary lamellae, and by further growth the 

 po&terior cardinal was developed. This would prove that (1) the 

 anterior and posterior laterals are the oldest teeth of the Bivalve 

 shell, and should therefore be present in the geological oldest species; 



(2) the anterior cardinal was formed afterwards, and is there- 

 fore younger than the laterals, but older than the posterior cardinal ; 



(3) the posterior cardinal was formed latest, and therefore must 

 be regarded as the youngest of all the teeth : geologically old 

 species could therefore have no posterior cardinal. 



Of the several primary lamella) those on the dorsal side of one 

 another appear to be older than the ventral lamellae, just as the 

 ventral portion of a bivalve shell is younger than the dorsal part, 

 according to the evident direction of growth in the shell. 



This relative development of the dorsal primary lamellae as older 

 than the ventrals is evident in the hinge of Pectuncidus and Area, as 

 given by Bernard, for the increase of lamellae takes place at the 

 ventral side of the first ; and the more lamellae which appear 

 ventrally, the more the older lamellae move directly and internally 

 until they disappear entirely. Thus the ventral primary lamellae are 

 the j'oungest ; and an increase of number takes place on tlie ventral 

 and not on the dorsal side. Shells having a hinge resulting from 

 the evolution of ventrally situated lamellae would therefore represent 

 a modern type ; whilst others, in which the hinge has developed 

 from the more dorsal lamellae, represent a more archaic type. 



Dr. IS^oetling states (page 0) that in examining the hinge of 

 several Recent and Miocene genera, represented by IS species 

 (described at pages 9-57, and illustrated on plates ii. to v., with 

 35 figures and 4 diagrams), on the basis of MM. Munier-Chalmas and 

 Bernard's methods, he has remarked some very noticeable features 

 in the development of the hinge of the Pelecypoda, 



