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



of these types, and probably the other is as deserving of 

 recognition. All of them range in diameter below 12.7 cm., 

 while some of them are considerably smaller, ranging down 

 to the diameter of 2.5 cm. Some of the specimens in the 

 collections of the University of California still retain the 

 original labels attached to them by Gabb or other members 

 of the State Geological Survey. 



The four succeeding types belong to the group 

 D. -planu latu ni . 



37. Desmoceras hoffmanni Gabb} 



Plate V, Figs. 120-123; Plate X, Figure 203. 



It is not easy to determine which of the several forms of 

 this group should bear the name proposed by Gabb. The 

 species described in Vol. II of the Paleontology of Cali- 

 fornia, and figured on Plate XX, which seems to belong to 

 another type, has not been thus far identified. 



In the collections of the University of California are 

 several specimens of a comparatively compressed shell, 

 some of which bear the name D. hoffmanni, and appear to 

 be referable to this species, except that the umbilicus is 

 somewhat narrower. Gabb states that in D. hoffmanni the 

 umbilicus has a diameter nearly equal to half that of the 

 coil. The six specimens here referred to this species have 

 a quite constant ratio between these measurements of 3.1:1, 

 the umbilicus being measured just inside the angles, or 

 shoulders. In the cross-section of the whorl they agree in 

 the main with Gabb's figure," though some of them are 

 relatively thicker. The number of constrictions does not 

 exceed seven or eight, though they are not regularly 

 disposed. The suture agrees in only a general way with 

 Gabb's figure, which is evidently defective. His descrip- 

 tion of the suture seems better, though it also is unsatisfac- 

 tory. The suture line consists of a siphonal and several 



iNoTE. — This species has been selected by Alpheus Hyatt for the type of a new 

 genus, Pleuropachydiscus of the family Silestidce (Eastman's Translation of Zittel's Paleon- 

 tology), but there is no apparent reason for such a classification, and paleontologists 

 who are most familiar with this species will probably accept it with hesitation. 



-'Pal. Cal., Vol. I, PI. II, figs. I3-I3a. 



