66 PALAEONTOLOGY OF CALIFORNIA. 



A. Rbmondii, n. s. 



PI. 12, Fig. 14, 14 a, and Fig. 15. 



Shell robust, discoidal. Whorls six or seven; enveloping 

 about one-third to two-fifths. Umbilicus about a third of the 

 whole diameter, rather deep, sides rounded. Sides of the whorls 

 somewhat flattened; dorsum broadly rounded. 



Surface exceedingly variable. One -form (Fig. 14) is orna- 

 mented by a few large, straight, or slightly sinuous ribs, which 

 arise in or on the margin of the umbilicus, and pass over the 

 sides and completely cross the dorsum. Between these are inter- 

 polated ribs, arising about the middle of the side, and crossing 

 the dorsum like the others. 



A second form has ribs, not more than half the width of the 

 preceding, sometimes dichotomous, and with several series of 

 nodes on the sides. 



Another variety is almost identical externally with A. Traskii, 

 Fig. 10, being ornamented by a series of ribs, which arise on 

 the margin of the umbilicus, and afterwards divide into from two 

 to five branches, which cross the dorsum. The septa are, how- 

 ever, markedly constant. Dorsal lobe broad above, narrower 

 below, a well-marked tongue between the branches, two spurs on 

 the outer side of each branch, and three above these. Dorsal 

 saddle occupying a third of the septum, deep, and divided into 

 two large and two smaller branches. Superior lateral lobe nearly 

 as wide as the dorsal, terminated by a trifurcate branch, with 

 four spurs above on the dorsal side and two on the ventral. 

 Lateral saddle deeply divided into two parts, each of which is 

 subdivided. Inferior lateral lobe very small, terminating in two 

 dentate spurs, and with two on the dorsal side. Two very small 

 supplementary lobes beyond these are merely dentate; the saddles 

 being equally simple. 



Fig. 14 is of the natural size. Fig. 15 is a part of a specimen, the outer whorl 

 of which is fifteen inches in diameter. 



Locality: North fork of Cottonwood Creek, Shasta County (Div. A.). 



