406 THE ZOOLOGIST. 



in London in 1883, when acting on one of the committees, we 

 had the pleasure of constant intercourse with the United States 

 representatives, among whom were Browne Goode and several 

 others of his scientific colleagues. Among the United States 

 exhibits of Economic Mollusca were specimens of the " Slipper 

 Shell" {Crepidula plajia) and the "Boat Shell" {C. fornicata). 

 These, however, did not then particularly attract attention. 

 In the Catalogue of Exhibits, though Lieut. Winslow, in allusion 

 to them, states that they " are neither directly injurious nor 

 beneficial, they are often associated with destructive Gastero- 

 pods. In addition, their absence from an Oyster-bed is one of 

 the many indications of its deterioration." He further remarks 

 that ** when present in large numbers they form one of the 

 indications of the health of an Oyster-bed." 



The above epoch-making Exhibition certainly gave a stimulus 

 to the consignment of American Oysters for replanting, for only 

 a few years previously had they been introduced to the market. 



The last to mention and doubtless the most important con- 

 tributions to the literature of the ** Slipper Limpets " are those 

 of Prof. E. G. Conklin (1897-98). The first memoir* deals 

 mainly with their embryology, and is illustrated, besides wood- 

 cuts, by nine large plates. His second paper t treats rather of 

 their Sexual Dimorphism, accompanied by three plates of re- 

 markable varieties of the shells of different species. 



As it is not our intention to enter into minutiae of the bio- 

 logical aspects of the molluscs in question other than what 

 applies to their influence on our fisheries, we shall only extract 

 (from Conklin) such points as have a bearing thereon. 



Referring to the New England species, C. fornicata, C. plana, 

 and C. convexa, he mentions they all show remarkable individual 

 differences in the shape of their shells. This, he avers, is 

 dependent on the shape and position of the mantle edge, which 

 moulds the shell to correspond with the surface upon which the 

 animal is attached. Hence it may be unusually broad and flat, 



* " The Embryology of Orepidula : a Contribution to the Cell Lineage 

 and Early Development of some Marine Gasteropods," Journ. of Mor- 

 phology, April, 1897, pp. 1-226, with nine plates and thirteen diagrams. 



f " Environmental and Sexual Dimorphism in Crepidula," Proc. Acad. 

 Nat. Sci. Philadelphia, 1898, pp. 435-444, with three plates. 



