42 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



collections leads very strongly to the belief that they are but dis- 

 torted representatives of the same zoological species I have called 

 N. corrugatus. 



But on this hypothesis it would not be correct to refer to these 

 species as varieties of N. corrugatus for there is no evidence to show 

 that the zoological species N. corrugatus expressed anything like 

 these divergences in form. 



Further, they are not imaginary species, for the characters they 

 express as fossils are as positive and real and exact as those expressed 

 by any other fossils. 



Nevertheless, taken separately, as figured and morphologically 

 described, there is nothing to indicate that they are not as "good" 

 species as any others described in this paper. 



They are, however, evidently distorted as is demonstrated by the 

 ollowing diagrams, which show the realtionship of the present form 



Fig. 1.— Axes of deformation in varieties of Nuculites. 



of each to the axis of general deformation of the splintery shales m 

 which they lie. 



The outline is here drawn as near as possible as it lay on the splint- 

 ery shale, the long axis of which is here placed horizontal and the 

 chief compression of which has been in a vertical direction. 



The line C-D is, for each specimen, approximately its long trans- 

 verse axis and A-B its vertical axis running through the tip of the 

 beak, on the supposition that they were originally normal shaped 

 specimens of Nuculites. 



Taking these three specimens to be actually three distorted indi- 

 viduals of the same species, a study of the effects of the pressure and 

 movement of the rock upon the original form is instructive. 



In the first figure {N. cThrysippus) the squeezing has changed the 

 relations of the lines A-B to C-D from 90° for each arc to 145° for the 

 arcs A-D and B-C and 45° for the arcs D-B and A-C, thus relatively 

 shortening the height of the front and the back and lengthening the 

 hinge margin behind the beak and the front half of the base; redis- 

 tributing each of the elements of the cu-cumference without markedly 

 disturbing the general shape of the contour. The beak is shifted 

 forward to the extreme front and the clavicle is turned strongly 

 backward. 



