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



F. Freeh ^ has recently proposed to drop the family 

 Meekoceratidae and the genus Afeekoceras, dividing the 

 species belonging to that genus between Ophice7'as, Priono- 

 lobus, and Aspidites, although all these genera were de- 

 scribed after Meekoceras, which was first described in 1879, 

 and fully illustrated in 1880. Freeh's reasons for this 

 change were that Hyatt included in his original diagnosis 

 not only the three American species that differ in certain 

 important characters, but also foreign species later assigned 

 to Balatonites, Xenaspis, Hungarites, and Celtites. Of 

 course, it was a mistake to include these elements under 

 Meekoceras, but the citation of them as species under 

 Meekoceras did not make any confusion as to the limits of 

 the group. The three American species were fully de- 

 scribed and figured, and one of them was certainly the 

 type.^ The fact that later writers extended Meekoceras to 

 take in heterogeneous elements does not invalidate it. If 

 such a rule in nomenclature should be accepted, almost 

 every genus of ammonites would be thrown out, and a new 

 name substituted. 



As restricted in this paper, Aleekoceras is confined en- 

 tirely to the Lower Trias, in which horizon it is very 

 abundant in California, Idaho, India, and Siberia. 



Genus Meekoceras, s, str., Hyatt. 



Type, Meekoceras gracilitatis, White. 



The restricted genus is represented in America by a 

 large number of undescribed species, in addition to the 

 type. It is also common in Asia, some of the Asiatic spe- 

 cies being nearly allied to the American forms. 



Meekoceras gracilitatis White. 



Plate XLII, Figs. 1-4; Plate XLIII, Figs. 3-4. 



1879. Meekoceras gracilitatis. White, Bull. U. S. Geol. Sur. Terr. Vol. V. 

 p. 114. 



iLethsea Palseozoica, Bd. II, Lieferung 4, 1902, p. 630. 



* Professor Hyatt told the writer, in June 1900, that he had regarded Meekoceras 

 gracilitatis as the type. 



