NO. 2225. NUCULITES FROM THE MAINE SILURIAN— WILLIAMS. 41 

 NUCULITES THYESTES, new species. 



Plate 11, fig. 8. 



Nuculites thyestes has a broadly ovate form; the length is about 

 one-tliird greater than the height, valves depressed-convex, beak low, 

 and (when viewed in such a position that the Hne connecting the mid- 

 dle of the anterior with the middle of the posterior end is horizontal), 

 the beak is decidedly posterior to the center. From this point of 

 view, the anterior end is evenly curved and is very broad, and the 

 posterior end is short and not more than half the height of the front. 

 The hinge is not in evidence, but the posterior slope indicates the 

 position of the beak, and there is a gradually broadening furrow 

 separating two very low umbonal ridges. The clavicle is short, reach- 

 ing about one-third the distance to the margin and slants forward. 

 The surface markings are the same as for N. chrysippus and N. atreus. 

 Dim.ensions, greatest diameter 21^ mm. (which is on the line con- 

 necting the center of posterior end with center of anterior end); 

 height 17 mm. (79 per cent). 



Formation and locality. — Pembroke formation, sphntery gi-ay shales 

 in the southern part of West Pembroke, on west side of Pennamquam 

 River (loc. No 1.45.6 A). 



Type-specimen.— Ciit. No. 62884, U.S.N.M. 



REMARKS ON N. CHRYSIPPUS, N. ATREUS, AND N. THYESTES. 



These three quite dissimilar shells, found in a small outcrop of the 

 splintery Pembroke shales in West Pembroke village, offer some par- 

 ticularly interesting facts for the paleontologist. 



They are represented by figure 8 on plate 11, and figures 3 and 5 

 on plate 12. 



At first glance they appear to represent three distinct genera neither 

 of which is Nuculites. On closer inspection, however, a slender clav- 

 icle is discovered on each specimen and on one of them the charac- 

 teristic crenulations are seen, so that upon comparing them with 

 fuller collections of Nuculites from other outcrops of the Pembroke 

 shales, it is clear that each of them is a distorted specimen of some 

 species of Nuculites. 



The three forms are so decidedly different that, from a morphologic 

 point of view, they must be regarded as distinct species. In order to 

 discuss them, I have given them names: 



M 1787 = Nuculites clirysippus (pi. 12, fig. 5). 



M 1788= A^. atreus (pi. 12, fig. 3). 



M 1789= 7y^. thyestes (pi. 11, fig. 8). 



Although neither of the forms has any near resemblance to N. 

 corrugatus, nor has there been found in this locality any specimen 

 that can be referred morphologically to that species, a study of the 



