144 TWENTIETH ANNUAL REPORT OF THE REGENTS. 



The extreme form of the loop noticed in those from the Shaly limestones 

 would indicate that there would also be considerable difference in the soft 

 parts of the animal, from those with shorter loops; and it then becomes a 

 question as to what changes these parts of a species can undergo. The 

 external form of those from this position is not very unlike those from the 

 Niagara group of Lockport, N. Y., except in generally being more yentri- 

 cose ; that one seldom becoming gibbose. From those occurring at Wal- 

 dron, Ind., it varies in the finer striae, and in the inequality of the valves. 

 The Upper Helderberg specimens from the Falls of Ohio scarcely vary 

 externally from those of the shales of the Hamilton group of New York, 

 except in the coarser striae, but very materially in the spires. 



I have not been al)le to examine any European specimens of ^. reticula'' 

 ris ; nor have I found any American examples of A. asjyera in a condition 

 to show their internal characters, unless the A. spinosa of Hall can be 

 considered as of that species, which is scarcely probable. 



NOTE. 



The foregoing article was prepar(>d^for the Regents' Report on the State 

 Cabinet, as communicated to the Legislature April 2d; but owing to the 

 delay in printing, and the amount- of material to be set up before it, it has 

 been detained until the present date. During the autumn I visited several 

 localities of the Hamilton group in Northern Iowa ; at one- of which 

 (Waverly) I saw numbers of specimens of Atr^^pa showing sections of the 

 spires, and I observed that the volutions composing the cones vary in 

 number with the increase in age and size of the shell ; while specimens of 

 the same size have about the same number of volutions. I might also 

 mention in this connection, that Prof. Hall has in his possession a small 

 specimen of A. nodostriata, sent to him by Dr. Rominger, which had 

 been cut to show the spires ; but not far enough to reveal the loop ; but by 

 cutting a little more, I found the loop well preserved. It is comparatively 

 strong, and has considerable forward curvature. The spires have only six 

 volutions, owing probably to the immature condition of the shell. 



EXPLANATION OF PLATE I. 



Fig. 1. View of a specimen of Atrypa reticularis from the Lower Helderberg group 

 of Albany county, N. Y., showing the form and position of the loop and spires. 

 The view is obliquely from above and behind. Enlarged. 



Fig. 2. Interior of a ventral valve; from the same position andlocality as the last, 

 enlarged to show the depressed area and solid beak. 



Fig. 3. Interior of a ventral valve of J. reticularis from the Hamilton shales, 

 showing the form of the beak as existing in very perfect specimens; for com- 

 parison with fig. 2. The specimen is in Prof. Hall's collection, and the figure 

 borrowed from the Pal. of N. T., Vol. IV. 



Fig. 4. An enlarged outline figure of the first volutions of the spires with the loop 

 and crura, attached to the hinge-plate. The specimen from which the figure 

 Avas drawn is from the Falls of Ohio, and belongs to the collection of Prof. 

 Hall, from whom it was obtained for manipulation. 



Figs. 5 & 6. Dorsal and ventral views of a specimen from the shales of the Hamil- 

 ton group of New York, showing the form of spires and loop. 



Figs. 7 & 8. Dorsal and ventral views of a specimen of Atnjpa spinosa, Hall, from 

 the Hamilton shales of New York, showing the form of spires and loop. Figs. 

 4 — 8 are natura' size. 



