FOURTH, OK CORONICERAN BRANCH. 191 



well with those of latum, and lead us to hope that this may prove to be the adult. 

 Certainly it is very distinct from the true Bucklandi, and the characteristics, so 

 far as shown, are such as one might expect in the first senile stages of Cor. latum. 



Coroniceras Bucklandi, Hyatt. 



Plate III. Fig. 18. Summ. PI. XII. Fig. 17. 



Amm. Bucklandi, Sow., Mill. Conch., II. p. 69, pi. cxxx. 



Amm. Bucklandi, Ziet., Verst. Wiirt., pi. xxvii. fig. 1. 



Amm. Bucklandi, Phill., Geol. York., p. 1, pi. xiv. fig. 13. 



Ariel. Bucklandi, Wright, Lias. Aram., p. 269, pi. i. fig. 1-3. 



Amm. Bucklandi, Quenst., Amm. Schwab. Jura, pi. ix. fig. 1 (not fig. 2, 3). 



Amm. Bucklandi costaries, Quenst., Ibid., pi. xi. fig. 1. 



Amm. solarium, Quenst., Ibid , pi. viii. fig. 1-3. 



Amm. sinemuriensis, D'Orb., Terr. Jurass. Ceph., p. 303, pi. xcv. fig. 1. 



Amm. sinemuriensis, Quenst., Amm. Schwab. Jura, pi. xi. fig. 18-20. 



Cor. sinemuriense, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 78. 



Localities. — Lyme Regis, Semur, Basle, Aargau, Scheppenstadt, Schaichhof, Balingen, Tubingen. 

 Var. sinemuriense. 



Plate III. Fig. 18. 



This has young which closely resembles the young of Cor. latum. The breadth 

 of the abdomen, divergent sides, ininiature folds, and tubercles are quite similar. 

 The folds also begin with large tubercles on the first part of the second whorl. 

 On the third quarter of the third whorl the true pilae begin. After this the 

 abdomen no longer increases so fast in breadth, and finally, upon the latter part 

 of this volution, or the beginning of the fourth, this region is hardly wider than 

 the dorsum, and the sides flattened. On the first or second quarter of the fourth 

 whorl the pilae become duplicate or triplicate, and the broad, thin, abdominally 

 projecting tubercles characteristic of this species arise. These peculiar pilae and 

 tubercles occur, in some specimens, intercalated with single pilae and tuberculated 

 geniculae bending forward upon the abdomen. The keel on the third quarter of 

 the third whorl was well developed, and must have appeared considerably earlier. 

 The channels were but slightly developed on the first quarter of the fourth whorl, 

 though they have well defined ridges, and probably began later than the keel, 

 somewhere perhaps upon the last half of the third volution ; but this could not be 

 ascertained with certainty. One specimen from Semur had but two divided pilae 

 upon the third whorl ; after this they remained single to the fifth volution, the 

 last observed. D'Orbigny's figure of Amm. sinemuriensis was taken from a young 

 individual of about five and a half whorls, in which the pilae are all divided. This 

 is as exceptional in the species as are the specimens without any divided pilae. 



The superior lateral saddles are much narrower than the inferior laterals. 

 The abdominal lobe is about one half longer than the superior laterals. 



A fine specimen of this species from Semur, Plate III. Fig. 18, retains the 

 peculiar characteristics of sinemuriense for five and a half volutions, with a similar 

 rate of increase, and slightly divergent or flattened sides. These sides become 

 then more rounded, the pilae single, parting with their tubercles ; and on the 

 eighth volution, or perhaps sooner, the whorl assumes all the characteristics of 



