OF CONCHOLOGY. 



125 



it remains to apply the information gained to the combination of 

 the several forms. 



1st. In the number, position and direction of the primary spines, 

 and in the form of the aperture, there is a close and essential 

 similarity between P. lambis, P. hryonia, P. crocata, P. scorpnis, 

 P.pseudoscorpio, P. 77iilUpeda, P. vioJacea and P. ehngata. 



2d. On the other hand, in all such respects, P. cMragra and 

 P. rugosa differ very much from the others and equally closely 

 agree with each other. 



As to the intercalary spines, the extreme species of the first of 

 such groups differ widely, but are connected by a series of species 

 exhibiting intermediate character. 



As to lip surface, there is likewise a considerable difference 

 between the extreme species of the same group, but between 

 such are interposed the species P. violacea and P. wilUpeda. 



In the second group the two species exhibit almost equally 

 great difference in the character of the lip surface, although in 

 other respects so closely allied. 



It will be apparent that there is no coincidence between the 

 development of the wrinkled lip surface and of the intercalary 

 spines, unless indeed it be admitted that the dentiform labral 

 lobes of P. scorpius and P. pseudoscor'pio are spines. Such an 

 admission would, however, be a virtual confession of the insig- 

 nificant value of the development of the intercalary spines. On 

 the other hand, the comparison of P. violacea with P. millipeda 

 and of P. chiragra with P. rugosa, attest to the slight value of 

 the presence or absence of the rugosities as distinctive of natural 

 groups. 



Full consideration would therefore appear to necessitate the 

 combination of P. lambis and those already enumerated as asso- 

 ciates in one natural group, and of P. cldragra and P. rugosa, 

 in another, and in accordance with the prevalent valuation of 

 groups, such would seem to be well entitled to generic rank. 

 What names such genera should bear must be a subject for special 

 investigation, and a review of the literary history is requisite. 



§ 3. History. 

 The founder of the binomial nomenclature associated all the 

 species known to him, as well as representatives of the genus 

 Aporrhais and of Rostellaria in the genus Stromhus, in a sec- 

 tion (the first or " Digitati "), characterized by the digitated lip. 

 The genus was first subdivided by a binomial systematist, in 

 1797, — Humphrey, in the " Museum calonmanum," published 

 in that year, combining together the species of the section Digi- 

 tati of Linnd, and reserving for it the name Stromhus, while for 

 those with a simple lip he proposed the name Alatus, but neither 



