— 58 — 



When still larger the whole of the ribs and interspaces are covered with 

 riblets, as in P. subnodosus {Liropecten veatchii Gabb), and many others. 

 Conrad's supposition that "X. rolsej'crmis^'' must have one flat valve, i 

 only based on the fact that his convex valve was unusually convex, as 

 often found in this species, while the transverse lines on the ribs are 

 also found where the shells grew too crowded. His "i. crassicardo ^ ' 

 was an old specimen, having more riblets and a stronger hinge, and 

 really represents the left valve of the species. In the one figured here 

 there is scarcely any difference in thei convexity of the two valves, but 

 it is rarely found with both together, and sometimes they occur unequal 

 or both much flatter, which often arises from pressure since fossilization. 

 The distinctive characters of Liropecten are in the strongly-toothed 

 hinge, approaching that of Spondyhts, and this was finally admitted by 

 Conrad as a character common to them all, when he included them in 

 that new genus. The great convexity of the valves in two of his 

 "species" is due to what he calls "undulation," but is a kind of 

 imbrication, as shown in the figure. It is not a natural character, being 

 never twice alike, but seems to have been caused by some unfavorable 



condition of growth. It is sometimes seen in living species, and on the 



other hand fossil Liropectens sometimes grew without it, as shown in 



his figure of L. crassicardo. 



The pair of valves is well represented just as it was found; the ears 



are from another specimen, which is of the original estrellanus form. 



Found in Coast Range Tertiary from Oregon to Santa Rosa Island, 



Calif., but not farther southward. 



Note. — In the Catalogue of Californian Fossils, published in the Seventh 



Annual Report of State Mineralogist, 1887, p. 246, the form Liropecten 



volseformis Con. is given as living on west coast of Mexico, and probably 



the same as L. subnodosus Sowerby, 1835. This reference was intended 



for L. veatchii Gabb, but was accidentally misplaced. 



FOSSILS FROM COLORADO DESERT, COLLECTED BY H. W. 



FAIRBANKS. 



These were collected only near Carrizo Creek where it emerges from 

 the mountains forming the western rim of the desert, and are of more 

 than usual interest. Many collectors have been to the same locality 

 and obtained the Tertiary species described by Conrad thirty-six years 

 ago, as well as the Quaternary fresh-water shells of the recent lake-bed, 

 most of which still live elsewhere. Loose species of fossiliferous rock of 

 Carboniferous age are also found, but none in place, in that vicinity. 

 The chief interest of Mr. Fairbanks' collection is the discovery of what 

 may be called fossil coral-islands, the coral forming extensive beds 

 about the summits of short isolated ridges detached from the mountains 



