LOWER SILURIC SHALES OF THE MOHAWK VALLEY II3 



acter, and the mature conch transverse sharp striae, about four to 

 the millimeter; the neanic conch exhibits an intersecting system of 

 both, visible to the naked eye, while on the mature conch still 

 shadowlike traces of the longitudinal lines are visible under the lens. 



Formation and locality. In the Canajoharie shale at Alplaus 

 creek, Saratoga county, N. Y., and other places. 



Remarks. This species is easily recognized by three characters ; 

 its slender, slightly curved shell, the closely arranged septa and the 

 delicate surface sculpture. 



The specimens are all more or less crushed, and the septa mostly 

 dissolved and the conch filled with shale. We have, therefore, been 

 unable to satisfy ourselves completely as to the generic determina- 

 tion of the species, and we do not know whether it is a true 

 Orthoceras or not. On account of the relative width of the siphuncle 

 it approaches Baltoceras. 



The surface sculpture corresponds exactly to that of E n d o - 

 ceras proteiforme var. tenuitextum, var. 

 tenuistriatum and 1 i n e o 1 a t u m Hall, as described in 

 Palaeontology of New York, volume i. These Trenton forms do 

 not belong to Endoceras proteiforme but are orthocera- 

 tites that need revision. Also the common and often cited ''Endo- 

 ceras proteiforme "of the Utica slate (title 3, plate 85, 

 figure I ) belongs in the same group which eventually will be referred 

 to, we believe, as Orthoceras tenuitextum Hall. They 

 all have the same rate of growth, the same closely set septa and the 

 same characteristic surface sculpture. We would also have referred 

 the species here described to Hall's species if it were not for the 

 curvature of the conch. 



A species identical with our type save its coarse cancellated 

 sculpture, has been described by Walcott (title 9, page 22) as O. 

 oneidense from the Utica shale of Trenton, N. Y. 



The most interesting feature of the material from the Alplaus 

 creek is the presence of the embryo shells or protoconchs on the 

 partly pyritized and partly calcified nepionic portions of the conchs 

 (see plate 8, figures 4, 5). 



The history of the investigation of the protoconch of the ortho- 

 ceratites is a very interesting one. Branca considered as the 

 embryonal shell or protoconch the cup-shaped termination of the 

 conch as usually found. Hyatt viewed this chamber as the first 

 chamber and the cicatrix which it generally bears upon its distal 

 surface as the remnant of the protoconch. The latter was figured by 



