GENEALOGY. 59 
have any, though, as in the keelless tortilis form, the abdomen may become 
elevated, or very slightly subangular. Wright’s figure’ admirably illustrates 
such an individual. The Sironotus variety figured by D’Orbigny has a more 
compressed form and an earlier development of the keel. 
Second Subseries. — Caloceras laqueum has many varieties. First, those which 
develop the keel at a very late period of the growth, and grade into the third 
variety of Cal. tortile. With these we find, as sub-varieties, some which, either 
immediately before or at the time when the keel is developed, change by growth 
the general form of the whorl. The abdomen may become elevated, as in the 
first senile stage of some varieties of ¢ortile, or depressed, assuming the aspect of 
carusense or spiratissimum. Secondly, those which develop a keel at a comparatively 
early stage, and either retain the rounded sides, or become subquadragonal and 
approximate in form and pilx to Ver. spiratissimum? 
The senile whorl had metamorphoses, which produced an elevated or narrow 
abdomen, similar to that of Cad. tortile at the same stage, though in some varieties 
the sides were flatter, and there is a nearer approximation to the true trigonal 
outlines of the old of Vermiceras. 
The young of carusense*® repeated the characteristics of the intermediate forms, 
but generally produced the keel at earlier periods. These are also lowest in 
geological position, and pass into otuer varieties, occurring later geologically, 
which are of much larger size. In all these larger specimens‘ the form is notice- 
ably subquadragonal in the adult, and also has a keel, and sometimes faint 
channels. There is a tendency in old age to produce a rounded whorl, with an 
elevated angular abdomen in the clinologic stage, resembling the same part in 
the old age of the prominently keeled varieties of tortie and nodotianum. In 
the large variety of carusense we also find some forms which in their clinologic 
stage have flattened and convergent sides, with a keel and slight channels. In 
other words, there are some specimens which show a tendency in old age to 
change the subquadragonal form of the adult, very much as in the genus Ver- 
miceras. In this species, also, the sutures were observed in one case of extreme 
age to lose the differentiated proportions of the adult, and partially retrograde, 
becoming similar to those of Psiloceras.’ The: young and the adult of many 
specimens of the raricostalum variety of earusense® are inseparable from the same 
stages in the extreme of variety a of raricostatum,' with the exception perhaps of 
slight differences in the marginal digitations. 
The typical raricostatum,’ however, is not similar to Cul. Liasicum, being ex- 
tremely broad transversely, and having a very immature gibbous whorl, which can 
be called subquadragonal only in variety 4. In old age,’ even the broad whorl of 
the typical variety diminished in transverse diameter, the abdomen became more 
elevated, and the‘keel and pile obsolescent, until finally a fragment of the old 
whorl cannot be distinguished from the same stage of Cal. tortie or nodotianum.”” 
1 Lias Amm., Pal. Soc., I. p. 316, pl. xvi. 2 Summ. Pl. xi. fig. 22. 
8 Summ. Pl. xi. fig. 15. fore uoiged3, 
6 Pl. ii. fig. 3, 8 a. 6 Pl. i. fig. 16. T Pl vie fig. 15. 
Sha fig. 20 a: 9 Pl. i. fig. 24, 25. 
10 Compare section of old nodotianum, pl. i. fig. 10, with section of old raricostatum, fig. 25. 
