308 On Prophysaon, etc. 



plate from the middle begius to cover the second, the fifth covers half of 

 the fourth, and the succeeding plates always more, until the last covers 

 two-thirds of the preceding one." 



The formula of the lingual membrane is given by Schacko 

 as being one hundred and fourteen rows of 19-1-19 ; by 

 Morse of Lea's species, fifty-one rows ot 13-1-13. 



The centrals of H. pygmoea are said by Schacko to be tri- 

 cuspid ; the two side centrals so small, and scarcely recog- 

 nizable, that they entirely disappeared in one specimen ; the 

 laterals bicuspid. He remarks that every tooth of the 

 radula lies alone, so that even the cusps do not cover or 

 disturb the basal surfaces of the overlying rows. 



Scjhacko refers to the near alliance, in form of jaw espec- 

 ially, of H. pygmma with H. minutissima of the genus 

 Panctiim of Morse. 



Looking at the descriptions and figures of the jaws of 

 jpygmoea and minulissitna, we notice, with striking general 

 similarity of characters, some differences ; on the other hand 

 the lingual teeth of the two forms appear to be the same, and 

 the shells without variation of specific value. 



The facts regarding the distribution of H. pygmcea, which 

 may be treated as one of the circumpolar species, ftivor the 

 opinion, which we are disposed to adopt, that Lea's specific 

 name must be placed in the synonymy of Punclum pyg- 

 moeiim. 



The species known as //. pygmcea, Drap., has an extensive 

 range in northern (Lapland, Denmark, etc.) and central 

 Europe. The North American form occurs in California, 

 also in Maine, Massachusetts, New York and Ohio, and has 

 lately been discovered by Mr. Hugo W. Ericsson, in Bosque 

 County, Texas. 



Oeooialsiciis maculosus, Allm. 



On p. 293 of this article we compared Propliysaon with 

 the Irish genus Geomcilacus^ as far as known to us by pub- 



