:I43 



;i. Area elongate, not distinctly triangular, at least 5 times as long as 

 wide. 



a) Apex prolonged, recurved. Outline not strongly transverse ; 



<7rr/;/^?(:-/ MuRCHisoN. 



b) Apex less prolonged, slightly recurved over the area ; outline 

 strongly transverse (width equal at least to times the 

 length) : siihcxtcnsus Mx\rteu,i. 



c) Apex shortest, acute, upright. Area lineal. Maximum breadth 

 of the shell in its visceral part ; shell depressed : vicari n. f. 



2. Area distinctly triangular, with length equal to 2—4 times the width 

 apex not prolonged over the area, upright, acute : 



siib-arcJdaci Martpxli. 



; B. Shell large, globular, with a large and strongly recurved apex ; area high, 

 with a large delthyrium of equilateral triangle : gvrtani n.f. 



II. Cardinal line elongate ; shell winged. Outline of the typical form 

 trapezoidal. Width equal to 1^2^ times the length. 



A. Area elongate, linal, many times longer than high. Apex small, less 

 prolonged, a little recurved : lonsdalci Murchison. 



B. Area triangular, from 3 to 6 times as long as wide. Apex upright, acute 

 not prominent over the area ; vernenili Murchison. 

 If one compares these two tables of classification, one will be convinced 



at once that the latter is by far the more exhaustive, many points being taken 

 into account one by one by the Italian naturalist besides the form of the shell. 



It is not quite safe to judge of the true characteristics of a fossil merely 

 from pictures and descriptions ; but if the two classifications can be compared 

 something like the following relations will be found to exist between the 

 varieties of Pellizzari and the groups ofGossELEx. 



Pellizzaui. Gosselet. 



var. archiaci Murch. 



var. siibcxtensiis Mart. Fig. 10 obovati. 



24 hemicycli. 



25 



. 2S 



-var. vicari Ym.uz. 36 (?j obovati. 



