DESCRIPTIONS OF UPPER JURA FOSSILS — AMMONITIN^. 421 



would be called open umbilici. The keel is prominent and deeply crenu- 

 lated. It is separated from the genicul^e by narrow channels, which are 

 not crossed by bifurcations of the costse, as in more generalized species 

 of this genus. The serrations of the keel appear to be separated by the 

 channels from the costse. 



The sutures were present, and, although much distorted, it was ascer- 

 tained that they had large first lateral saddles and lobes, with smaller 

 second lateral saddles and small second lateral lobes. There are aux- 

 iliary saddles on the umbilical shoulder, and the abdominal lobe is 

 shorter than the first lateral lobes. These sutures are decidedly cardio- 

 ceran. There is in the Museum of the Mining Bureau at San Francisco 

 a fine specimen (no. 11953) of this species collected,* also in Calaveras 

 county, which is associated with a fragment of some species of Aucella, 

 and one in the collection of the United States Geological Survey has a 

 fragment of what is apparently a variety of Aucella erringtoni on the 

 same slab. All its closest affines are in the Upper Jura, and the com- 

 parisons made below show that it is not a species of Pleuroceras, the only 

 genus in the Lower Jura which contains similar forms. 



Species of Pleuroceras show their derivation from such forms as 

 Pleuroceras hawskerense by their coarsely costated and heavily tubercu- 

 lated young whorls, but the costa3 of this species are linear even in the 

 young. The sutures of Pleuroceras are also decidedly Arietian, having a 

 long, narrow abdominal lobe longer than the first lateral lobes, a pair of 

 very large, broad first lateral saddles, and broad first lateral lobes, with 

 second lateral lobes and saddles showing on the sides, all of these being 

 but slightly cut into by the outlines of the minor or marginal lobes and 

 saddles. C. duhium cannot, therefore, be considered a species of Pleuro- 

 ceras of the Lower Jura. 



Cardioceras (Ammonites) beaucjrandl, sp. Sauv.f This species is similar 

 in aspect, but has not distinct channels and has incomplete subsidiary 

 alternate costie between the longer ones. Cardioceras aliernans, sp. Von 

 Buch, is a polymorphic species as usually defined, and has flat-sided, 

 flat-abdomened discoidal forms, and also varieties that are more invo- 

 lute and compressed. Most of the forms, especially of southern Europe, 

 have bifurcated costa^, but there are some specimens of all varieties show- 

 ing the late development of single costiB in adults. These correspond in 

 their characters to the neanic stage of Cardioceras duhium, having similar 

 keels, channels and outline. 



*Two miles west of Motherlode, Texas ranch, six miles north of Copperopolis, one-half mile 

 below stage road from Capperopolis to Sonoraand two and a half miles west of the month of Angels 

 creek. Collector, Dr C. D. Voy. 



t Jour, de Conch., vol. xix, xx, p. 165, pi. 10, and also as figured by De Loriol, Mem. Soe. Phys. 

 Geneve, vol. xxiii, pi. 2, fig. 4. 



