198 



MAirUAL OF THE MOLLUSC A. 



Distribution, about TOO species. Trias — Chalk. Coast of 

 Chili (D'Orbigny), Santa Fe de Bogota (Hopkins), New Jersey, 

 Europe, South India, and New Zealand. 



In this, as in almost every case, the figures represent the 

 number of species which have been described, and which gene- 

 rally pass current as species. It is very probable that when all 

 the forms have been thoroughly examined many may turn out 

 to be nothing more than variations of the same species, due to 

 differences of age, &c. Thus, according to Mr. Seeley, the Am- 

 monites splendens from the greensand of Cambridge, comprises 

 not only the form so-named, but fourteen others occurring in 

 the same bed, and which have received distinctive specific names; 

 A. planulatus is made up of five so-called species. Looked at 

 from this point of view the TOO would be replaced by a much 

 smaller number. 



Captain Alexander Gerard discovered ammonites similar to 

 our L. oolitic species, in the high passes of the Himalaya, 16,200 

 feet above the sea. 



Section A. Back with an entire Tceel. 



1. Arietes, L. oolites, A. bifrons (PL III., Fig. 6), bisul- 



catus (PI. III., Fig. Y). 



2. Falciferi, L. oolites, A. serpentinus, radians, hecticus. 



3. Cristafi, cretaceous, A. cristatus, rostratus (Fig. 62), 



varians. 



I 



4. Amalthei, ool. 



0. Bothomagenses, cret. 



6. JDisd, 



7. Dentati, 



B. Back crenated. 



A. amaltheus, cordatus, excavatus. 



A. rothomagensis, from Bothoma- 



gum, Eouen(Pl. III., Fig. 4). 



0. Back sJiarp. 

 oolitic, A. discus, clypeiformis. 



D. Back channelled. 

 I cret. A. dentatus, lautus. 



I ool. 



A. Parkinsoni, anguliferus. 



