270 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



lihabdopleura, etc., are so much more intimate with each oth- 

 er than in either case with other branches, it is considered 

 advisable to represent such relations by the combination of 

 the groups into one great primary type. 

 In the Mollusca vera are three classes : 



1. Cephalopoda, with two orders Dibranchiata and Te- 

 trabranchiata. 



2. Gasteropoda, with five sub-classes and eleven orders: 

 Diceca, with JPectinibraricMata, Heteropoda, Rhipidoglossa, 

 Docoglossa, and Polyplacophora ; Pulmonifera, with Ptd- 

 monata ; Opisthobranchiata, with 2ectibranchiata and Nu- 

 dibranchiata ; Pteropoda, with Thecosomata and Gymnoso- 

 mata ; Prosopocephala, with Solenoconchw (Deritalium) 

 only. 



3. Conchifera, with five orders: Dlmyaria, Metarrldptaz, 

 JTeteromyarta, Monomyaria, and Rudista. 



These three classes contain 283 families, recent and fossil. 

 The remaining three classes and nine orders, constituting the 

 3folluscoidea, embrace 73 families. 



AMERICAN OYSTERS IN ENGLAND. 



Mr. Frank Buckland, in Land and Water, refers to some 

 " Saddle Rock" oysters which a friend had just sent him from 

 New York. They were pronounced by the critic to be white, 

 fat, and plump, and altogether first-class eating, with, how- 

 ever, a slight " mussel" taste about them. According to Mr. 

 Buckland, the proper way of packing oysters, so as to keep 

 them for a long time, is to place them carefully with the con- 

 cave shell downward, by which means the moisture is all 

 preserved, and the breathing apparatus is kept moist by the 

 natural fluid. 2 A, December 16, 1871, 419. 



ORIGIN OF PEARLS IN OYSTERS. 



According to Mr. Garner, in a paper read before the Lin- 

 nsean Society, the production of pearls in oysters and other 

 mollusks is caused by the irritation produced by the attacks 

 of the minute entozoon known as Distoma ; and he thinks 

 that by artificial means the abundance of this parasite may 

 be greatly increased. British pearls are obtained mostly 

 from species of Unio, Anodon, and Mytilus, but it is proba- 

 ble that all mollusks, whether bivalve or univalve,, with a na- 



