23 



specimen collofted. Six otltcrs were olttained ; one a very immature 

 individual. al»out an ineli and a quarter in diameter; and live of an in- 

 termetliate and almost unitbrm size, wliicli measure from two to two and 

 a half inches across. The smallest shell is entirelj^ smooth ; the medium 

 sized ones are only faintly sti'iated across the wliorls. These latter 

 differ from the specimen tigured, in the following- respects: they are 

 much thinner and flatter proportionately, their pei'ipher}^ is nari'ower, 

 and their umldlicus is .smaller as Avell as shallower. Such half- 

 grown shells resemble the Ammonites Hdydenii of Gabb very closely, 

 but their periphery is not " nearly fiat " and somewhat squared, 

 as it is in that species, but narrowly and evenly rounded. Externally 

 there are very few characters by which they may be distinguished, 

 but the septation is said to be different in Californian examples of the 

 two species. The septa are not visible in an}' of Mr. Richardson's 

 specimens. 



2. Dwarfed costate variety. — Figs. 3 and 3a on Plate 1. represent the 

 most perfect specimen obtained of this form, the other being a mere 

 fragment, Its greatest diameter is two inches and five lines : the width 

 of its umbilicus, eight or nine lines: the maximum thickness, seven lines. 

 The fossil is, however, considerably distorted. It differs from the more 

 typical form less in shape than in sculpture. The latter consists 

 of simple, transverse and flexuous, ribdike folds, which are most 

 prominent on the outer half of the sides. They form distinct, 

 narrowly rounded, convex arches over the perijjhery and are faintest 

 near the uml)ilicus. The elevations are usually narrower than 

 the shallowh" concave grooves Avhich separate them. Sometimes a short 

 rib occurs between two of the ordinary ones, but when this is the case it 

 generall}' forms a short arch over the periphery and does not reach to the 

 umbilicus. The folds also show a tendency to bifurcate over the per- 

 iphery, and there are some other unimportant and exceptional variations. 

 The greatest thickness of the whorls in this variety is a little above the 

 middle of the sides. 



Ainmonites Breicerii was first described from the "Shasta Group"' of 

 Cottonwood Creek, Shasta Count}', California, where it appears to be 

 tolerably abundant. Uiitil Mr. Eichardson collected the specimens de- 

 scribed above from the Islands in Skidegate Channel, the sjiecies had not 

 been obtained from any other locality. 



Ammonites difficilis of D'Oi'bigny, a French Neocomian fossil, is its 

 nearest Eui-opean representative. B(jth A. difficilis and A. Brewerii are 

 very abnormal representatives of the Cl3'peiformes, but as D'Orbigny and 



