NAPLES FAUNA IN WESTERN NEW YORK, PART 2 22*1 



and that the stages of torsion of the Lunulicardium shell in subse- 

 sequent growth are indicative of its phylogenic stages of progress toward 

 the monomyarian stock. This conclusion is based wholly on external 

 characters and the fact of actual observed torsion in the shell from youth 

 to adulthood. The Protoconchae being theoretically the primitive lamelli- 

 branch condition, we may never come to know it except in this manifesta- 

 tion. It is well to add that the supposed position of the pallial line in 

 this group, just within the hinge, is a feature on which the nature of 

 our material permits no observation. 



As to the systematic position of Lunulicardium it seems to us probable 

 that its ancestry may be found in the Ambonychias and Byssonychias of the 

 Lower Siluric ; we should be disposed to hold it probable at least that the 

 shells represent a departure from the aviculoid stock in which the anterior 

 adductor is lost either by fusion with the posterior or by suppression. 

 Neumayr was disposed to derive from Lunulicardium the peculiar genus 

 Conocardium, and Beushausen has contributed a considerable body of facts 

 supporting this proposition, describing a genus Conocardiopsis, which to 

 him indicates a passage phase between the two genera. Having stated the 

 reasons for our inability to conceive of Lunulicardium precisely as construed 

 by Beushausen, we shall take occasion to remark that the genera which 

 have been proposed as subdivisions of the old term, viz, Chaenocardiola 

 Holzapfel and Prochasma Beushausen, seem to lack substantial grounds 

 for recognition, except in so far as these terms express extremes of develop- 

 ment in one direction and another. Forms referable to both of these 

 genera in outline, character of surface, length of lunule, occur in abundance 

 among our species, but so far as our observation extends, they are all 

 opisthogyre and all constructed on the same plan. 



We note the proposed subdivisions which have been made of this 

 genus Lunulicardium. 



Pinnopsis Hall, 1843. This name was introduced by Hall in the 

 Geology of New York (report on fourth district), for the species P o rn at a 

 and P. acutirostrum from the Portage (Naples) shales of western New 



