THIRD, OE VEEMICEEAJST BEANCH. 139 



the usual stout smooth whorl of the young of Johnstoni. Quenstedt places them 

 with laqueus, but this, we think, is a mistake, arising from not giving proper 

 weight to the characteristics of the nealogic stages. 



The presence of this form in the North German basin is worthy of remark, 

 since it is a degraded variety. The transitional keelless varieties uniting this 

 species and Johnstoni would have been considered distinct under the name tortile, 

 while the keeled forms would have been separated and designated as a distinct 

 species, but for the fact that similar variations are also represented within two 

 other species, Gal. Liasicum and JVodotianum. It is evident from this, that the 

 keel in Caloceras has not become an hereditary character, but is a morphological 

 equivalent in varieties of different species. 



Caloceras Liasicum. 



Amm. Liasicus, D'Orb , Pal. Fran. Ceph., I. pi. xlviii. * 



Amm. Liasicus, Hauer, Ceph. Lias Nordostl. Alpen, pi. iii. fig. 1-3. 



Amm. sironotus, Qoenst., Handb. Pet., p. 432, pi. xxxvii. fig. 1; and Die Amm. Schwab. Jura, p. 23, pi. i. 



fig. 21. 

 Amm. laqueolus, Schlon"., Paleontogr. , XIII. pi. xxvi. fig. 1. 

 JEijoc. laqueolus, Wright, Lias Amm., p. 315. 

 JEyoc. Liasicum, Wright, Ibid., pi. xv. fig. 1, 2 ; pi. xvi. fig. 1, 2. 

 JEgoc. tortile, Wright, Ibid., pi. xv. fig. 10, 12. 

 Ariel. Liasicus, Wah., Unt. Lias, Mojsis. et Neum., Beitr., VI., 1887, pi. xx. fig. 1-5. 



Localities. — Semur, Bristol. 



A large specimen in the Tubingen collection, about 100 mm. in diameter, 

 shows by comparison with D'Orbigny's figure that sironotus, Quenst., is prob- 

 ably identical. One specimen at Semur retained very gibbous sides and broad 

 abdomen to a diameter of 175 mm., and then formed an elevated abdomen with- 

 out acquiring a true keel as figured by D'Orbigny. Another shell had reached 

 the diameter of 260 mm., but no true keel was formed, though old age began to 

 show its approach in the obsolescence of the pike. In D'Orbigny's collection 

 these very broad forms stand side by side with the narrow one figured by him, 

 which is identical Avith sironotus, Quenst. D'Orbigny's original has the keel as 

 well developed at a diameter of 100 mm. as the broad variety at a diameter of 

 250 mm. A comparison of the young with the young of tortile showed that they 

 are closely allied by their development. No constant distinction exists, except 

 that Liasicum is usually a stouter shell, and has about the same relation to tortile 

 that the stouter forms of carusense in the Upper Bucklandi bed have to those of 

 the same name in lower beds. Wahner's work upon this species gives figures of 

 the young, and exhibits a close alliance with Gal. Johnstoni. The keel appears 

 in his Figure 3 b, in a small but probably full-grown specimen, but no channels 

 are noted in his figures or description. 



The extraordinary series of forms discovered by Neumayr and Wahner in 

 the Northeastern Alps enable us to give the following list of species, arranged 

 in subseries. 



