NO. 2225. NUCULITES FROM THE MAINE SILURIAN— WILLIAMS. 35 



This outcrop is believed to represent the uppermost beds of the 

 Edmunds. 



Remarks. — The discovery that specimens, from the Crowe Neck 

 locahty, Edmunds formation, in other respects having the characters 

 of N. corrugatus, are crossed upon the umbonal ridge and slope by 

 distmct fine radiating lines suggests intimate genetic relationship 

 between the two species. 



From a morphologic point of view N. subplmius and N. corrugatus 

 are two distinct species. The fact that the radiating hnes on the 

 posterior end of the shell occur only in this Crowe Neck locality, sug- 

 gests that they are a matter of preservation rather than of specific 

 distinction. 



From a taxonomic point of view, if the radiating lines be given 

 specific value, then N. suhplanus becomes the type of the Crowe 

 Neck forms and the more elongate forms which in other respects 

 agree with the typical N. corrugatus of the Leighton Cove locality 

 become varieties of N. suhplanus distinguished from N. corrugatus 

 by the radiating lines. 



With this interpretation the Leighton Cove (Pembroke) species 

 N. corrugatus becomes the later representative of the Edmunds, 

 Crowe Neck, species N. suhpilanus from which it differs by absence 

 of the radiating lines on the posterior end of the shell. 



Type-specimen. —Cat. No. 62874, U.S.N.M. 



NUCULITES TRESCOTTI, new species. 



Plate 12, fig. 1. 



SheU obliquely ovate; front end short, narrowly rounded; pos- 

 terior end large, subcuneate, produced both downward and back- 

 ward. Beak prominent, arching over the hinge and terminating 

 near the front. Valves convex, most so over the central portion. 

 Umbonal ridge prominent, subangular, below and anterior to which 

 is a well-defined depressed furrow extending from posterior side of 

 beak obliquely across to the post-inferior margin. Basal margin 

 broadly rounded from the front to the umbonal furrow, where it 

 turns upward to form a distinct reentrant sinus. Hinge short, with 

 crenulate teeth (evident behind the beak); the posterior margin, 

 from the end of the hinge to top of the umbonal ridge, long and 

 nearly straight. The cardinal slope abrupt and slightly concave. 

 Surface crossed by sharp, fine concentric lines. The clavicle is 

 approximately vertical to the hinge line, well defined, but slender, 

 and in some specimens distinctly curved as in Nuculites triqueter 

 Conrad . 



The long axis, from the center of the front margin to extremity of 

 the postumbonal ridge, cuts the shell into two approximately equal 

 portions; the arched basal margin protruding below to balance the 



