NO. 2225. NUCULITES FROM THE MAINE SILURIAN— WILLIAMS. 47 



posterior slope between the sinus and the cardinal margin. Surface 

 very finely striated. A slender clavicle extends from the anterior 

 cardinal margin a little more than halfway to the base, and curving 

 slightly forward. 



Arisaig, coU. J. W. D. 



In the first place, Nuculites lentus has crenulate hmge teeth. The 

 genus Clidojpliorus was, in its original definition, distinguished from 

 Nuculites by the absence of crenidation upon the hinge. The appli- 

 cation of the generic name Glidophorus to the species C. elongatus thus 

 distinguishes the two species. 



In our figure 6 (pi. 12) the two valves of the same shell are together, 

 and comparison with Hall's figure shows that the right valve is nar- 

 rower while the left valve is broader than his figure. The difference 

 between the two valves is, however, clearly a matter of distortion. 

 Figure 13 shows a specimen which differs from C. elongatus in the 

 broader, less extended, posterior end; both of our figured specimens 

 show the preumbonal furrow to be less strongly marked than in G. 

 elongatus, and the beak is also broader and less conspicuous. The 

 clavicle of N. lentus is apparently more slender and straighter than 

 that of C. elongatus. The specific definition of the latter, however, is 

 in aU its particulars broad enough to include such specimens as iV. 

 lentus and not specific enough to exclude them. 



Formation and locality. — Edmmids formation, gray shales on shore 

 of small cove in northeast part of Crowe ISeck forming the northern 

 extremity of Straight Bay, Trescott Township, near the dividing line 

 between the Edmunds and Pembroke formations, classified as Ed- 

 munds in the Eastport folio (loc. No. 5.33.8 A). 



Type-specimens. — Cat. No. 62891 U.S.N.M. 



ON THE INTERPRETATION OF FOSSILS. 



In selecting Nuculites corrugatus for description, and in writing the 

 description of the species, the chief purpose was to present to the 

 reader the characteristic fossils of the several formations which were 

 being mapped in the Eastport Folio. 



It was a species met with in several of the outcrops of the Leighton 

 member of the Pembroke formation and in one exposure of the Ed- 

 munds formation, which latter, by its fauna as well as position, was 

 interpreted to be at the top of the Edmunds formation. 



Specimens from the typical locality were found to express consid- 

 erable variation in form. Two specimens (one transversely elongate 

 and the other much shorter and higher in form) were selected to 

 express this variability. In this description, therefore, several of 

 the characters regarded as of specific value were described as varying 

 in presence or absence or in strength of expression of the characters. 



In this method of species-description I was following rules very 

 commonly adopted by expert paleontologists. 



