300 NATURAL SCIENCE [May 



seeing that its hinge, like the Tertiary genus Wooclia, Desh., combines 

 cardinal teeth of the heterodont type, with laterals that recall those 

 of the Anisomyaria and even the Taxodonta. 



NoETH Ameeican Copepods of the Genus Diaptomus 



The Illinois State Laboratory of Natural History has lately issued 

 another of its very useful little Bulletins dealing with North Ameri- 

 can fresh-water Invertebrates. It treats of the genus Diaptomus 

 and is essentially a systematic paper, appealing mainly to students 

 of the Copepoda. But it also brings out a point of some general 

 importance, namely, that not one of the twenty-two species described 

 occurs in any part of Europe. This is a very remarkable fact when 

 it is remembered that nearly all the North American species of the 

 genus CycloiJs, and more than fifty per cent, of the fresh-water 

 Ostracoda and Cladocera are common to North America and Europe, 

 It looks very much as if, notwithstanding a continuous process of 

 intermingling of the majority of the Entomostraca of the two con- 

 tinents, the American forms of Diaptomus have been effectively 

 isolated from all European influences for a sufficiently long time to 

 allow of the development of an entirely new set of species. This, 

 of course, implies that the Atlantic forms an impassable barrier to 

 the latter, but that it does not seriously affect the active dispersal 

 of the Entomostraca as a whole, and it also probaljly implies that 

 the comparatively short time (geologically) which has elapsed since 

 the breaking up of the northern land connection between America 

 and Europe has been sufficient for the production of great difference 

 in the Diaptomus faunas of the two continents which now exists. 



Some Eemakkable Eaewigs 



Among recent contributions to the life-histories of insects, none will 

 prove more interesting than the paper by Mr E. E. Green, which 

 was read before the Entomological Society last March. About two 

 years previously the author had exhibited to the Society some 

 remarkable insects from Ceylon, which he believed to be later stages 

 in the development of the species figured and described by Westwood 

 in 1881 under the name of Dyscritina longisetosa. Westwood was 

 unable to assign a definite systematic position to his new genus, the 

 type of which was a small insect, somewhat resembling an earwig, 

 but provided with two long slender tail-filaments, each of which was 

 about three times the length of the creature's own body, and made 

 up of about fifty minute segments. Mr Green was able to shew by 

 means of drawings that, except for the segmented tail-appendages, the 

 insects he exhibited possessed all the characters of true earwigs, and 

 he ventured to express an opinion, in which he was supported by 

 Mr Gahan, that these insects represented larval stages of forms 



