po CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



siigatiim^ Placenticeras californicitm, P. pacijicicm, and 

 other Lower Chico forms. 



31. Hamites (Ptychoceras) aequicostatum Gabb. 



Ptychoceras cBquicostaticm Gabb, Pal. Cal., Vol. I, p. 74, PI. XIII, fig. 20; 

 Vol. II, PI. XXV, figs. 20, e and /. '^o\. Helicancylus cequicostatus Gabb, 

 Pal. Cal., Vol. II, p. 141, PI. XXV, figs. 20, a-d. 



Ptychoceras ceqtiicostatuni , as originally described by 

 Gabb, is a true representative of this genus, and usually 

 not difficult to recognize as such; it is not uncommon in 

 the Upper Cretaceous beds of Shasta County. 



On the larger branch of the shell the transverse ribbing is rather heavy, 

 and without ornamentation; the ribs themselves are high and narrow, the 

 intervening spaces rather broad and concave. On the smaller branch the 

 ribs are much less prominent, and the intervening spaces correspondingly 

 shallow; many of the ribs, at least, are ornamented with lateral, mammillary 

 tuf)ercles. Between tlie ribs which are so ornamented there are subordinate 

 ridges that appear to be simple; and with these there are also subordinate 

 striations. 



These markings can be detected on Gabb's types and on 

 other examples which are among the collections of the 

 University of California. 



In Gabb's revised description of this species ' quite another 

 genus (which Zittel refers to L.indigia, with some doubt) 

 has been confused with this species, and both are placed in 

 the genus Hclicancylus. 



32. Hamites (Ptychoceras) solanoense, sp. nov. 



Plate IX, Fig. 184. 



Shell of moderate size; smaller branch of the type 15.5 cm. in length, with 

 an average diameter of 14 mm. ; tapering very gradually from small end to 

 the recurved portion; surface marked by regular, simple, and rounded trans- 

 verse ribs which are almost without ornamentation. There are seventy-five 

 of these ribs on the whole length of the small branch, evenly distributed 

 throughout. The only ornamentation noticed on these ribs are rows of very 

 faint tubercules on the ventral surface, on either side of the median plane, 

 most noticeable near the curve. On the dorsal side, which is somewhat 

 flattened, the ribs are nearly suppressed. On the recurved portion they are 

 also apparently less prominent. 



li'al. Cal., Vol. II, 1863, p. 141. See also Lindigia ? nodosum, this paper, page 92. 



