LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

description of species 171
above, border bearing somewhat thickened umbilical ribs; septa as shown in tbe
figure; ribs often dividing.
The holotype (Calif. Acad. Sci. type Coll.) was found by Andrew McFarland on
Alderson Creek, about 2 miles south of Ono, Shasta County. It baa the following
dimensions: greater diameter, 209.5 mm.; width of umbilicus, 58 mm.; ratio, .277:1,
height of whorl, 60 mm ; ratio, .429:1; width of whorl, 75 mm.; ratio, .382:1.
According to accounts given by tbe discoverer the holotype was found at a horizon
somewhat above the Argonaut zone in beds referable to an upper Aptian stage. No
more exact statement of its occurrence can now be given.
Aeanthoplites Sinzow
Among the large number of parahoplitid forms described by Anthula (1000, p.
102-119), from the Caucasus Mountains, Sinzow (1907, p. 478-508) has distinguished
a group lor which he has established the genus AtanOioplibx. In this group tho
whorls are more compressed, the umbilicus broader, and the venter more rounded
than Parahoplitet Anthula, wherein it seems to retain characters of Parahopliioidee
Spath. The genotype of this group is "Parahoplites" aachillacntie (Anthula).
Under the genus Acanlhoplilu Sinzow has figured and described as many as 15
different forms which he regards as distinct species. Many of these forms in their
young stages possess characters of Acanihoceraa or of DouiriUciceraa, such as spines,
or tuberculeB on the umbilical borders or at the point of division of the ribs. These
features are usually lost in tbe older stages of growth, and in some cases new features
are acquired, as happens in. other groups.
In the middle and upper parts of tbe Horsetown group (upper Aptian to middle
Albian) similar forms are abundant and include many apccios that may be regarded
as analogues of those found in the Caucasus regions. Some of these will be noted
as such in the descriptions, although materials are not yet at hand for a completes
account of all of them. In their younger stages some of them approach, or perhaps
retain, characters of Parohoplites or even young examples of PttTakopliUidtt, on the
one band, and on the other have the apinose ornamentation of Chelcnictras or Douvilleicerai
and without the mature shells they may easily be mistaken for such. In
fact, in the past, some have been referred to A cattihoceraa and Douiiifciccraj.
Acanthopliies aegis Anderson, n. sp.
(Plum ID, &gura 1}
Shell large, diseoidal, moderately involute, umbilicus moderately broad, sides
cloaely costate, about 64 ribs on the last whorl of the holotype; ribs rounded, slightly
sinuous, sometimes single, more often divided, crossing the periphery without weakening
or flattening; umbilicus bordered by low, Abrupt walls, upon which arise the
primary riba; periphery rounded. Thia species resembles Parahoplitca slanloni
nov. but it is readily distinguished by ita broader umbilicus, relatively thinner section,
and its fewer and broader riba. The holotype (Calif. Acad. Sci. type Coll.)
affords tbe following measurements: greatest diameter, 235 mm.; width of umbilicus,
05 mm.; heightof whorl, 85 mm.; thickness of whorl, fift mm.; umbilical ratio, 0.404:1,
The holotype was found by Andrew McFarland on Alderson Creek, 3 miles south of
Ono, Shasta County. It represents the upper middle Horsetown group, locality
1348 (Calif. Acad. Sci.). Its autural characters are not unlike those of Parahoplites.
This is not the largest representative of the genus found, but in diameter it approaches
the largest. Smaller examples of the species have been foqnd higher in
tbe section, near the top of the Cottonwood heds, or at the base of the Hulen beds,
on the Hulen Creek drainage.