FOURTH, OR CORONICERAN BRANCH. 165 
Var. C; 
The whorls are stouter than in variety B, and acquire on the first quarter 
of the fourth whorl, or later, a close resemblance to those of semécostatum. The 
inferior lateral saddles are considerably deeper than the superior laterals, the 
inferior lateral lobes considerably shorter than the superior laterals, and pointed. 
The sutures were observed upon the latter part of the fifth whorl. 
SECOND SUBSERIES. 
Arnioceras semicostatum, Hyarr. 
Plate Il. Fig. 10-16. Summ. Pl. XII. Fig. 4. 
Amm. semicostatus, Simpson, Amm. of Yorkshire Lias, p. 51.1 
Ariet. semicostatus, Wrieut, Lias Amm., pl. i. fig. 7 (not fig. 4, 5, 8). 
Arn. semicostatum, Hyarr, Bull. Mus. Comp. Zodl., I., No. 5, p. 74. 
Localities. — Whitby, Semur, Basle, Spezia. 
Var. A. 
Plate II. Fig. 10, 16. 
During the first four and three quarters or five volutions, the shell closely 
resembles Arn. miserabile, var. acutidorsale. After this the pile appear. They are 
at first broad and depressed, but possess the sharp definition of true pile, and 
terminate abruptly on the edge of the abdomen. The abdomen is rounded, and 
the keel a distinct though depressed ridge. Its time of appearance could not be 
determined, but it was plainly apparent on the second or third quarter of the 
fifth whorl, and previous to this the aspect of the abdomen was precisely that of 
nuserabile, var. acutidorsale. 
Var. B. 
Plate II. Fig. 11-14. 
In this variety the young resemble veryclosely the adults of Arn. miserabile, 
var. acutidorsale. The pile make their appearance earlier than in variety A, but, 
while becoming more numerous, often retain their fold-like aspect, and terminate 
abruptly near the abdomen. The keel appears about the same time as the pile, 
and may be either with or without slight channels. In some specimens the 
whorls become stouter than usual in the adult, and the genicule prominent. In 
one specimen they are inclined posteriorly. 
In the Museum of Stuttgardt there are three specimens of this variety, one 
from Behla and one from Muhlfingen (No. 4688), both in the Geometricus or 
Upper Bucklandi bed. Another from Filder was found in the Angulatus bed. 
1 This name does not appear in the first edition of Morris’s Catalogue, 1848, but is found in the second 
edition, 1854, as Amm. semicostatum, Y. & B., Geol. Yorkshire, p. 257. This is an erroneous reference, since 
no such species was described in that work. In the Museum of Yorkshire is a specimen with this name, and 
it was described by Simpson in his Monograph of the Ammonites of the Yorkshire Lias, which was not cited 
in Mr. Morris’s first edition, though published in 1843. . 
