126 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



Many of them are very beautiful. Numerous fossils from the same 

 locality were seen in the Museum at Constance. 



From the Miocene to the Pleistocene, we know little of the 

 American insect fauna; but the interglacial clays have yielded a 

 number of Coleoptera, which Scudder has described, rinding them 

 distinct from, but closely allied to, living species. As the Pleisto- 

 cene plants are known to be mostly living species, it appears from 

 this that the species of insects change more rapidly than those of 

 flowering plants; but generic changes among insects appear to be 

 very slow. Most of the multitudinous species .of insects which 

 perplex entomologists may be said to be due to a sort of shuffling 

 of the characters which have been inherent in their several generic 

 types for a very long while. 



-In discussion of Professor Cockerell's paper Dr. Gill objected 

 to the liberal use of the word cockroach and added that he had 

 argued this point with the late Dr. S. H. Scudder. His objection to 

 Professor Cockerell's use of the term was that the ancient insects 

 called cockroaches were not the cockroaches of today; they do not 

 belong to the family Blattidse or even to the same order as the 

 modern cockroaches which did not appear until the Upper Creta- 

 ceous. Dr. Gill added that he had made the same objection to 

 the common liberal use of the word " horse" as applied to the an- 

 cestors of the horse, stating that the three-toed horse was not a 

 horse or even closely related to the modern Equus -indeed it be- 

 longed to an entirely different group. 



Dr. Gill added that among most animals there was a great dif 

 ference between the ancient types represented in the Palaeozoic 

 formation and those which come in the Cretaceous and newer 

 rocks. So marked is the difference that for mammals the modern 

 fauna has no family in common with the Eocene except possibly the 

 Didelphidids. The difference is not so well marked in the molluscs 

 as they have come through with but little change since the Creta- 

 ceous, and even earlier, for there are several freshwater types, as 

 viviparids, melaniids, unionids, in the Jurassic beds which on the 

 characters available can hardly be distinguished from forms living 

 today. The mammals are entirely different and have evolved very 

 rapidly, the fish less rapidly, and the molluscs more slowly, so these 

 great goups may serve as chronometers for the including rocks. 



