19S 



MANUAL OF THE MOLLUSCA. 



Distribution, about 700 species. Trias — Chalk. Coast of 

 Chili (D'Orbigny), Santa Ee 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 

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

 Tuonites 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 700 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 luitli an entire heel. 



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



catus (PI. III., Fig. 7). 



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



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



varians. 



B. Bach crenated. 



4. Amalthei, ool. 



5. Bothomagenses, cret. 



A. amaltheus, cordatus, excavatus. 



A, rothomagensis, from Bothoma- 



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







C. 



Bach sliarp. 



6. 



Disci, 



oolitic, 



A. discus, clypeiformis. 







D. 



Bach cJiannelled. 



7. 



Dentati, 



j cret. 

 ]ool. 



A. dentatus, lautus. 



A. Parkinsoni, anguliferus. 







E. 



Bach squared. 



8. 



9. 



10. 



Armati, 



Capricorni, 



Ornati, 



L. ool. 

 L. ool. 

 ool. 



A. armatus, athletus, perarmatus. 

 A. capricornus, planicostatus. 

 A. Duncani, spinosus (PI. III., 

 Eig. o). 



