384 Analj/sis of Periodical Works 



placing these solitary shells as connecting species, instead of 

 connecting genera, between Limnea and P/it/sa. We would, 

 however, recommend the perusal of Mr. Sowerby's observa- 

 tions, which are drawn up with great clearness. Ten very ac- 

 curate figures are given of as many species, but only two of 

 these are accompanied by descriptions. Anastoma : a genus 

 formed of the Helix ringens of Linngeus, and a Helix we wish 

 it to remain, thougli it has had various other names, and the 

 small variety has been made into another species ; we consider it 

 a variety, because we know that in this, and other Helices, the 

 number of teeth is always inclined to vary. Gi-ycymeris : 

 the habits of this shell, when compared with many Solens, will 

 bring the two genera as closely as possible together, and So- 

 lenimya, as Mr. S. conjectures, should range in the same group. 

 Lithotryra: this is a very extraordinary genus, quite new to 

 us, belonging to the Linnasan Barnacles, and to Lamarck's 

 class of Cirripedes. Mr. S. gives a detailed accoimt of the 

 only species he has met with, accompanied by the following 

 generic character: — Testa irregulariter subpyramidalis, lateri- 

 bus compressis, pedunculo tubuloso tendineoque imposita, 

 octovalvis; valvis contiguis, injequalibus, lateribus sex, infe- 

 rioribus minimis ; dorsali magna, ligulata, antica minutissima. 

 Appendix testacea patellam inversam referens, ad basim pe- 

 dunculi. Animal intermedium inter sessiles et pedunculatos 

 Cirripedes, saxorum cavos ab ipso terebratos incolens. 



From these characters the structure, as we think, will be 

 found at variance with the idea that the animal is able to pierce 

 a deep cavity in limestone rocks; for, as it is elevated on a 

 peduncle, it must in that case detach itself from some other 

 substance, work with its head downwards to permit its coming 

 in contact with the rock, and then again reverse itself, and fix 

 its seat in the bottom of the cavity : all this, we conceive, is 

 highly improbable, if not impossible. We have learnt that all 

 tlie specimens which have been brought to England, were 

 procured from one rock at Montserrat; and our present 

 belief is, that they belong to a species exclusively inhabiting 

 the deserted cavities previously made in rocks by the Pliola- 

 daricc; precisely in the same manner as the Hermit Crab takes 

 up its abode in empty shells. We do not, however, wish this 

 opinion to be implicitly believed, but merely offer it as the 

 most probable of the two, and until further information may sup- 

 ply the place of conjecture on this very interesting subject. 

 Mr. Sowerby animadverts, with great reason, on the strange 

 and even absurd idea of making Otion (a Linnaean Barnacle) 

 a bivalve shell, because it has only two valves ! Crenatula: 

 a genus vei-y well defined, and with two excellent figures. 

 Perna : Mr. S. is not aware that this genus was one of the 



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