270 PROCEEDINGS OF THE ACADEMY OF [Feb., 



before me 32 mm., width 8 mm. On the part of the larger body 

 whorls below the shoulder, the revolving lyrae become more widely 

 separated, with three fine threads intermediate, as a rule, but the 

 lyrae are always flattened and in more or less low relief. 



Pleurotoma Mlgardi n. sp. 



From the Jacksonian of Moody's Branch, I have two species which 

 appear to have been confounded with servata, though differing radi- 

 cally therefrom in the structure of the nucleus. One, named as above, 

 is almost similar to servata in size, form and in the number and form of 

 the slightly oblique rounded ribs, but has the raised revolving lines 

 some eleven or twelve in number, subequal in size among themselves 

 and becoming only slightly larger on the anterior parts of the whorl. 

 The nucleus differs very radically from that of servata or ohlivia^ 

 being small, obtuse and composed of only one and a half to two whorls. 

 The canal also is decidedly shorter. Length 16 mm., width 5 mm. 



Pleurotoma coUaris n. sp. 



This is the second species from Moody's Branch referred to under 

 the preceding description. It is stouter, with a still shorter canal, 

 the aperture and canal together constituting about two-fifths 

 the entire length of the shell. The nucleus is small, obtuse and 

 of about two whorls. Body whorls about seven in number, each 

 with some seven or eight obtuse ribs and a wide and strongly elevated 

 conspicuous collar just below the suture, the upper sm'face of the 

 collar declivous to the suture and having two close-set revolving striae, 

 tlie lower part acutely elevated. The surface below the collar is deeply 

 concave, then rapidly expanding to the posterior of the three strong 

 raised hues which occupy about anterior half of the whorl. The 

 concavity is marked with many very fine close-set revolving lines and 

 the spaces between the three large lyrae referred to also have each about 

 three fine lines. Length 17 mm., width 6 mm. 



Pleurotoma arnica n. sp. 



Of the species allied to rotceelens and tenella, there are several 

 forms in the Red Bluff stratum. One of these, named as above, 

 is somewhat stout, sculptured nearly like rotoedens, excepting that 

 the concave and rapidly expanded surface immediately below the 

 sutural collar scarcely ever acquires more than about two fine threads 

 which occupy its median parts, while in rota^dens there are numerous 

 fine threads at this part of the larger whorls. The nucleus in eimica is 

 larger than \^ rotwdens, and there are generally about three of its whorls 

 covered with fine acutely raised riblets, instead of about two whorls, as 



