2i 



CHAPTER ill. 



OF THE TERMS USED IN DESCRIBING SHELLS. 



It is to be observed in explaining the terms made use of in 

 describing shells, that the same word has sometimes a very 

 different meaning from what it is intended to convey at others ; 

 but if the connection in which it is used is attended to, there 

 will seldom occur much difticvilty in knowing Ikav to under- 

 stand it. For instance, the term ovata occurs in the twelfth 

 edition of Systema Naturce, and in the eighth volume of the 

 Transactions of the Linnasan Society, in describing the form of 

 Mya trnncata and arenaria, and also of Bulla fontinalis and 

 Hypnorvm, although the first are of a very different shape from 

 the last. Also Cyprcca Onyx, C. Ziczac, &c. are said to be um- 

 bilicata, as well as Nerita Cmirena, glaucina, &c., though the 

 hollow which is called the umbilicus is so exceedingly different 

 in form and structure in the first from what it is in the last. 



OF BIVALVE SHELLS. 



First, of the Substance, which is either — 

 Crassus, thick, as Venus verrucosa. 

 Tenuis, thin, as Tellina depressa and Fahula. 

 Membranacea, thin like a skin, as Solen anatinus. 

 Fragilis, brittle, as Solen Legumen. 

 Pellucidus, transparent, as Tellina lactea and lacustris. 

 Opacus, opake, as Cardium edule. 

 Margaritaceus, pearly, as Mytilus margaritiferus. 



