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



while the corresponding width of the umbilicus is 5.7 cm. 

 The specimen is the inner coil of a much larger shell, 

 30 cm. in diameter. The aperture is not circular, but has 

 a width of 8.4 cm,, and a depth of 7 cm. In this specimen 

 the removal of one complete volution would reduce the 

 diameter to 3.3 cm. Another specimen of the same spe- 

 cies in the collections of the University of California, meas- 

 uring a little over 40 cm. in diameter, would, by the removal 

 of two complete volutions, be reduced to almost the same 

 dimensions, 3.3 cm. The aperture of this gigantic speci- 

 men measures 15 cm. in diameter. It does not contain the 

 whole of the body-chamber, which would have consider- 

 ably increased its diameter. This is evidently the species 

 represented by the specimen to which Gabb has alluded^ 

 as the "largest known species of California." It is not 

 very difficult to recognize even the young shells of this 

 species when compared with typical specimens of L. hatesi 

 of the same diameter, or of the same number of coils. A 

 specimen of this shell in the collections of the University of 

 California measures sixteen inches in greatest diameter. 



Occu7'rence. — This species is found in the upper portion 

 of the Horsetown, though its downward range is not known. 

 Dr. Smith states that he has found what is probably the 

 young of this species associated with Phylloceras ramostcm 

 Meek and P. ono'ense Stanton in the Lower Chico beds of 

 Arroyo del Valle, Alameda County, California. 



Lytoccras argonatitaj-tim, as Gabb has stated, is the 

 largest ammonite known from the Cretaceous of California. 

 The name is proposed in honor of the " argonauts " and 

 gold-seekers of the pioneer days of California and the 

 Pacific Coast. This gigantic cephalopod appropriately 

 commemorates the motive and heroic spirit of these sturdy 

 and brave adventurers who so often struggled with hard- 

 ships even greater than those described in traditionary 

 history. 



iPal. Cal., Vol. I, p. 67; Vol. II, p. 132. 



