(ill GENESIS OF THE AKIETID.E. 



Gal nodoiianum? as found at Semur, lias two varieties. One of these resembles 

 the subquadragonal varieties of Cal carusense until a late stage of development 

 with somewhat flattened sides, similar pike, keel, and faint channels. Afterwards 

 it assumed the more acute form of whorl characteristic of its own species. Gal. 

 sulcatum 2 is transitional to Gal. Deffneri in its characters, but is not very closely 

 allied. The sutures of Deffneri and its young form as seen from the side 

 appear to justify the position given it as the extreme form of the caloceran 

 series. In the Mediterranean province Gal. Johnstoni also occurs, and exhibits 

 transitional characters similar to those of the same species in Central Europe. 

 The pila3 are coarse, like those of the young in Psiloceras, and there is the same 

 tendency to an elevation of the abdomen, as in the same species in Central 

 Europe. Our remarks upon the subseries of this genus in the Northeastern 

 Alps are open to the objection that they were made upon the drawings of Neu- 

 mayr and Wahner, but our inferences do not differ widely from those of either 

 of these writers, except in the names given to the genera and in the rejection of 

 the name Arietites. We shall sufficiently discuss the details of the subseries 

 occurring in the Northeastern Alps under the heading " Caloceras," in the chap- 

 ter on " Descriptions of Genera and Species," and shall find that these in part 

 exist also in Western Europe. 



The first subseries in the Northeastern Alps contains the well known Cal 

 Johnstoni. This seems to be the immediate radical of a small series, consisting of 

 Gal hadroptychum, an unnamed form also figured by Wahner, and the giant Gal. 

 nigromonatum. The last has a keel, but no channels. 



This subseries also includes Cal. Liasicum, which is very close to Cal. Johnstoni, 

 LoM, and Seebachi, species having very immature keels, shallow channels, and 

 slightly depressed abdomens connecting Liasicum with Cal. Haueri of the next 

 subseries. 



The second subseries includes forms like Gal. proaries, which shows in its 

 development how closely they are all connected with Psiloceras and the forms 

 of the first subseries. This is the representative of Cal. nodotianum of Central 

 Europe, and a close ally of this species, though the young are apparently more 

 immature at the same age in the development of the keel and form of whorl. 

 Cal. gonioptychum appears to connect this with the extraordinary series of Cal. 

 cgcloides, Doetzkirchneri, Castagnolai, and abnormihbatum. This is peculiar to the 

 Mediterranean province, and shows that, like Psiloceras in the same region, Calo- 

 ceras probably had a complete cycle of forms, varying from the discoidal psiloce- 

 ratitic transitions with more or less elevated abdomens resembling Cal. Johnstoni 

 and tortile to Gal abnormilobatum, having complicated sutures, more involute, com- 

 pressed whorls, and a narrowed umbilicus. This series, however, though it 

 evolved an elevated acute keel in the two highest species, did not have deep 

 channels in any species. 



This subseries also contains Cal laqueum, var. scylla, and Cal. prespiratissimum, 

 two forms that approximate to Vermiceras in their characteristics. 



The third subseries arose apparently from Cal. Loki or Seebachi. The young 

 1 Summ ' P1 - xi - fig- 16. s Summ. PI. xi. fig. 20 ; 21. 



