46 
Dimensions. Holotype, a right valve seen from interior aspect — 
length, 115 mm.; height, 112; semidiameter, 11; hinge-line, 71. Paratype, 
a left valve, cast of interior — height, 118; semidiameter, 25; hinge-line, 78. 
Locality. Zone of aucella canadiana, west side of Harrison lake 350 
yards from shore and 1,400 yards north of Deer creek. 
Name. Generic and specific name after F. H. McLearn, palaeontolo- 
gist. 
Family, myalinidae 
Genus, Aucella Keyserling 
The species of Aucella from Harrison lake form a considerable and 
an important assemblage belonging to four separate hemerse. This was 
obvious at the beginning of this study, but at that time it was thought 
that the earliest Harrison forms corresponded to the earliest California 
Cretaceous species — Aucella piochii, and, in consequence, some mistaken 
identifications were made. Subsequently, larger collections and a more 
exhaustive study have shown that the species of the A. canadiana zone 
are later than A. piochii. Moreover, they are not related to that species 
but rather to the group of A. hononiensis. They seem to represent large 
shelled derivatives of this group evolved during the great expan five evolu- 
tion of Aucellae which occurred at the end of the Jurassic period. They 
represent one of the earliest Cretaceous hemerffi, probably that of Cras~ 
pedites stenomphalus. The other Harrison Aucellae, except A. kwoiekensis, 
belong to the period of restrictive and degenerative evolution of Polypty- 
ehites polyptychus and later time. 
Aucella acutistriata sp. nov. 
Plate IX, figure 2 
Resembles A. andersoni somewhat but differs in its much larger size 
and greater diameter. The ornament consists of concentric costae that 
are as sharp as knife-blades and stand 0-5 to 1 mm. above the general 
surface. They are spaced 8 or 9 in a cm. of radius. Become obsolete 
on anterior and posterior ends of shell which are striate concentrically. 
Dimensions. Holotype, a left valve — long axis, 78 mm,; short axis, 
that is the greatest line at right angles to the long axis, 42; semidiameter, 
28; apical angle, 69 degrees. Paratype, both valves in contact: left^ — long 
axis, 42; short axis, 25; semidiameter, 13; apical angle, 65 degrees; right- 
long axis, 39; short axis, 25; semidiameter, 11; apical angle, 80 degrees. 
Locality. Zone of Aucella canadiana, west side of Harrison lake, 350 
yards from shore and 1,200 yards north of Deer creek. 
Aucella catamorpha sp. nov. 
Plate IX, figure 5 
Very similar to the last except that the shell is unornamented. It is 
marked only by growth lines. Also the right valve has a more acute 
apical angle, and the diameter is slightly less. 
