426 A. HYATT — TRIAS AND JURA IN THE WESTERN STATES. 



j^j.'^qt^ Perisphinctes muhlbachi, n. s. 



Loc, near Greenwood, El Dorado county, California. 



The young are discoidal, but the increase in dorso-ventral diameters 

 is by no means so slow as in the normal forms of Perisphinctes. In the 

 large specimen which served as type of this description there were about 

 seven whorls, as* estimated, in a diameter for the whole shell of about 

 125 millimeters. 



The lateral costse are single, much coarser than in P. virgulatiformis 

 and very closely set. There were about forty-seven on the seventh whorl 

 and as many on the sixth. This gives the costse a more crowded aspect 

 on the inner whorls than on the outer one, the costations being wider 

 apart proportionately in the older stages than in the younger whorls. 

 The lateral costse are slightly arched forward, single, sharpl}^ defined and 

 prominent. The bifurcations are regular and set well upon the abdomen, 

 so that they are concealed, as in most of the species described in this 

 paper, by the involution of the whorls. The absence of straight, un- 

 bifurcated costse is noticeable in this species and P. filiplex (?), but the 

 latter has fewer costse and the bifurcations are not wholly hidden by the 

 involution of the whorls. 



The Whitney collection in Museum of Comparative Zoology contains 

 a water-worn specimen of this species without locality. The matrix in- 

 dicates, however, the same bed and it may be considered as Eldorado 

 county. A specimen collected by Dr Curtice on wagon road two miles 

 west ot Reynolds ferry and one mile west of the motherlode in Tuoluuine 

 county, California, is certainly very closely related to this species, but 

 the condition of the specimen does not permit a more positive opinion.' 



There are two specimens of milhlbachi in the Museum of the Mining 

 Bureau at San Francisco. Number 9020 is said to have come from Sailors 

 canyon. The matrix, however, is like that of the specimen from near 

 Greenwood, and Dr Curtice, having examined these examples, considers 

 the locality to be doubtful. They are probably from the same bed as 

 the typical specimen. The costse on the outer (sixth ?) whorl of the 

 largest specimen of these are more numerous apparently than in the 

 typical specimen, and in extreme old age the costse are single. 



No specimen has yet been recorded as having been found in place, but 

 the dark colored slate in which all specimens occur buried is identical 

 lithologically with that containing Belemnites from American canyon 

 near Greenwood, and the type specimen was picked up somewhere in 

 that vicinity. That it was not identical with P. skidegatensis, Whiteaves, 

 is evident from this description, that species having bifurcated costse 

 with incomplete, single abdominal costse between them. 



The type of this species was obtained by Mr Lindgren from Mr John 

 Miihlbach of Greenwood. 



