392 



NATURAL HISTORY OF ARTHROPODS. 



occur, however, in hot springs, and Hooker writes of a Himalayan species that was 

 found abundantly in springs which had a temperature of 112° F. Insects of this family 



respire, when under water, a sujiply of air which they 

 carry beneath their elytra, and which they renew, from 

 time to time, by coming to the surface, and resting 

 with the head hanging and the tij) of the abdomen just 

 at the surface of tlie water. Some of them remain 

 submerged an hour and a half, before renewing their 

 supjjly of air. The larger sj)ecies of Dytiscidie often 

 attack small fishes. 



The larvffi of the Dytiscidie, wliich are aquatic in 

 habits, and have free mouth-jiarts, five-jointed thoracic 

 legs, four-jointed antennje, and six pairs of ocelli, are 

 especially noticeable because their mandibles are hol- 

 low, and are consequently ada])ted both for seizing 

 their prey and for sucking out its juices. The mouth 

 cavity between the mandibles is not, as is often as- 

 serted, entirely closed. The larv.e resjiii-e by means of 

 two stigmata at the posterior end of the abdomen. 



Cybister has the suckers on the under side of the 

 tarsal disc alike, and arranged in four rows. C. fim- 

 briolatus, from the eastern United States, is greenish black, margined with yellow, 

 and is about 1.25 inches long. In Dytisais the suckers of the tarsal disc are of 

 different sizes, and the posterior stigmata are larger than in ('i/bisier ; the species are 

 all large. D. fasciventris, a species about 1.1 inches long, is common in Xew England, 

 and D. verticalis, about 1.3 inches long, is not very rare in the same region. Both are 

 black, with yellow lateral margins of the prothorax and elytra. In Europe D. viar- 

 ginalis, a species about the size of D. fasciventris, is the common one, and its larvje 

 attack young frogs, tritons, and fishes. 



The species of Acilius are of medium size, and have the posterior tarsi ciliate, the 

 claws of the same tarsi equal or nearly so. Many of the species have a yellowish band 

 across the posterior half of the elytra, and tranverse yellowish lines on the prothorax. 



Fig. 4C8. — Larva of Di/tisci(S. 



Fig. 469. — J/a(Ms 



bicarinatu^. 



. 470. — Rkmttus 

 )iotaHts. 



Kli;. 471.— //v''i".« 



Fig. 472. — Coptotomus 

 inten-of/atus. 



The tarsal discs of the males are round. A. fraternus is ^•ery common in New Eng- 

 land. Its length is about 0.6 of an inch, and the black portions of its elytra have a 

 yellowish tinge, due to the black consisting of very dense ]>unctures upon a yellow 

 surface. A. sulcatus is the common representative of this genus in Eurojie. 



In Hhantus the discs of the anterior tarsi of the males are oblong, and the elytra 

 smooth. Rhantus notatus, a species about 0.4 of an inch long, is found in Europe 



