144 GENESIS OF THE AEIETID^E. 



Caloceras Nodotianum, Hyatt. 



Plate I. Fig. 7 L 11 a. Summ. PI. XI. Fig. 16. 



Amm. Nodotianw, D'Orb., Terr. Jurass. Ceph., p. 198, pi. xlvii. 



Locality. — Semur. 



I have never seen the original, but the species as identified in D'Or- 

 bigny's collection and at the Museum of Semur, and also in Boucault's collection 

 named after D'Orbigny's types, has not a close resemblance to Oppel's type of 

 Nodotianum. This last is probably its morphological equivalent in the genus 

 Arnioceras, since it has smooth young, and is otherwise similar to Arnioceras. 

 A specimen in the Museum of Comparative Zoology, said to be from Semur, 

 has a stouter form and straighter pike than any specimen I have seen else- 

 Avhere. It has in these characters and in general aspect resemblances with 

 forms like Cal. proaries, var. latecarinatum, but the abdomen differs in not being 

 so much flattened. 



The fine suite of specimens in the Museum at Semur shows that this species 

 has several varieties. One resembles the variety of Cal. tortile from Walden- 

 burg. Another, at 128 mm. diameter, has the sides inclined and the abdomen 

 narrow, but not yet entirely acute. Another, even at the small diameter of 

 57 mm., has an abdomen acute, as is represented in D'Orbigny's figure. The 

 septal digitations of this species are not so complicated as in Liasicum or the 

 torus variety of Johnstoni. The examination of the specimens in the Museum 

 at Semur shows them to have been derived from Cal. carusense. The shells 

 found in the Tuberculatus bed resemble the adults of this species until a late 

 stage of growth. Plate I. Fig. 11, represents the full-grown adult, and Fig. 11 

 a section of the last whorl with its broad abdomen ; Fig. 7, a larger specimen ; 

 Fig. 9, 10, the approach of old age in a fragment of a still larger specimen. 

 In the section the abdomen is shown growing narrower on the last whorl. 



Caloceras raricostatum, Hyatt. 



Var. A. 



Plate VI. Fig. 15. 



Amm. raricostutus, D'Orb., Terr. Jurass. Ceph., p. 212, pi. liv. fig. 1, 2 (fig. 3, var. B). 



Amm. raricostatus, Quenst., Amm. Schwab. Jura, pi. xxiii. fig. 22, 23; pi. xxiv. fig. 4-10 (other figs., var. B). 



Ariet. raricostatus, Wright, Lias Amm., pi. vii. fig. 2-6 (pi. xxvi. fig. 5-14, var. B). 



Ophioceras Johnstoni, Hyatt, Bull. Mus. Comp. Zool., I., No. 5, p. 75. 



Localities. — Lyme Regis, Somerset, St. Thibault, Semur, Salins, Balingen, Boll, Willershausen in 

 Hanover. 



The pilae apparently begin abruptly, but they are really preceded by de- 

 pressed folds hardly perceptible to the naked eye. The pike are very closely 

 set at first, but begin to be more widely separated on the fifth or sixth whorl. 

 On the third or fourth whorl there are over forty, while on the eighth whorl 

 there are not over thirty. No other changes take place in them or in the 



