FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 221 



rounded. Beaks anterior or posterior to the middle of the length, often sub- 

 central. Cardinal line arcuate ; escutcheon marked. Surface marked by con- 

 centric striae, which, in some species, are regular and rugose. 



Hinge furnished with a triangular, spoon- shaped cartilage-pit beneath the 

 beaks, with a series of small transverse teeth on each side. There are two 

 principal muscular impressions in each valve, with usually a smaller retractor 

 scar adjacent, and also the cavity of the beaks often shows several pits for the 

 attachment of umbonal muscles. Pallial line simple. 



Examples : Nucula varicosa and N. randalli. (Copied from Hall's Lamelli- 

 branchiata.) 



NUCUla. Lamarck. 

 Etymology : nucula, a little nut. 



Nucula herzeri. N.SP. 



Shell small, elongate, sub- trigonal ; very gibbous.; length one and one-half 

 the height ; both terminal extremities very narrow, almost pointed ; beaks 

 prominent and closely incurved ; situated about one-fourth of the whole length 

 from the anterior end ; basal margin in its main portion only slightly convex, 

 even at its anterior end, where it joins the anterior margin, which is most 

 prominent close to the basal line ; at the posterior end the basal margin turns 

 in a light regular curve upwards to the very narrow, often pointed, posterior 

 margin. The cardinal margin slopes in a straight line down to the posterior 

 extremity, and with an inflected curve very abruptly to the anterior extremity ; 

 umbones very ventricose, making the thickness of the shell equal to its 

 height. 



This species is associated with Nuc. niotica and neda, which it resembles in 

 some points, but is easily distinguished from them by its elongate form, its 

 pointed terminal extremities, and the equality between its depth and height. 

 An average-sized specimen of this species has the following dimensions: length, 

 one-half inch; height and depth, one- third of an inch. 



Formation and Locality. Occurs in the cherty layers overlying the hydraulic cement rock of 

 the Devonian formation around the Falls of the Ohio in Kentucky and Indiana, I dedicate this pretty 

 little shell to Rev. H. Herzer, formerly of Louisville, Ky., who devoted his spare time to the study of 

 Natural Sciences, and especially to that of Palaeontology. It was 'he who rekindled in me the love for 

 Geology, which was almost extinguished by many years of hard work, but which since has afforded to mo 

 so many hours and days of genuine enjoyment. 



