ADDITIONS AND CORRECTIONS. 317 



distinctly elevated above the cardinal line j base nearly straight ; surface marking ob- 

 literated. 



This species approaches in form to the larger varieties of JV. levata, biit is more extended 

 posteriorly, and the anterior side proportionally shorter. 



It is not improbable but there may be two species among those given a.8 J^. levata, though 

 1 have not yet been able to distinguish them by decided characters. 



Fig. 3 a. Right valve of this species. 3 b. Cardinal view of the same. 



208. 9. MODIOLOPSIS AVICULOIDES (pag. 161, pi. 36, fig. 1 a). 



The transverse striae shown in this figure are due to pressure in the shaly matrix, which 

 produces markings similar to the " slickensides," or stria; made by the sliding of one 

 surface over another. Manv fossils in the Trenton limestone are thus marked. 



380. 6. BUCANIA INTEXTA (n. s;j.) 



Pl. XXXIII*. Fig. 4 a, b, c, d. 



Convolute, discoidal ; volutions three or more, contiguous, gradually expanding, the 

 last one continuing in a somewhat direct line to the aperture ; umbilicus broad and deep ; 

 back of the volutions broadly rounded ; sides obtusely angular ; dorsal line marked by a 

 sharp elevated carina ; surface of the shell ornamented by strong elevated longitudinal 

 striae, which are interrupted by distant oblique transverse lines, and crossed by finer stria;. 



This species, of which only a single fragment has been seen, was obtained by Dr. 

 Emmons, near Watertown, Jefferson county, in what he supposed to be the Trenton lime- 

 stone ; but from its close analogy with the B. sulcatina of the (/hazy limestone, I have 

 hesitated to place it with the Trenton species of the genus, fearing some error in regard to 

 its geological position. It diflers from B. sulcatina, in having the longitudinal grooves equal 

 to the stria; ; while in that one the elevated bands, which are often composed of two or 

 three smaller ones, are twice as wide as the spaces between. In addition to the fine obliquely 

 transverse striae, there are, at regular intervals, stronger ones which partially displace or 

 derange the longitudinal striae, so that they are not continuous. This character is less con- 

 spicuous in B. sulcatina. In that species, also, the dorsal line is depressed ; while in this 

 one it appears to have been carinatcd, a portion of the carina remaining. A comparison of 

 the figures of the surface of tlie two individuals will show the distinctions here indicated. 



Fig. 4 a. Dorsal view of the fragment. 



Fig. 4 b. Lateral view of the same. 



Fig. 4 c. A portion of the surface magnified. 



Fig. i d. K portion of the surface of B. sulcatina magnified. 



