574 



INSECTA. 



[XYL. 



villosus, Scudder, 1884, Mem. Bost. Soc. 



Nat. Hist., vol. 3, p. 291, Coal Meas. 

 XYLOBIUS, Dawson, 1860, Quar. Jonr. Geo. 

 Soc., vol. 16, p. 268. [Ety. xylobius, liv- 

 ing in wood.] Body crustaceous, cylin- 

 drical, elongate, rolling spirally ; seg- 

 ments thirty or more, anterior ones 

 smooth, posterior ones furrowed; legs 

 small, numerous; labrum quadrilateral, 

 divided by notches or joints into three 

 portions; mandibles two-jointed, last 

 ovate and pointed ; eyes ten or more on 

 each side. Type X. sigillarise. 



dawsoni, Scudder, 1868, Mem. Bost. Soc. 

 Nat. Hist., vol. 2, p. 236, and Acad. 

 Geol., p. 496, Coal Meas. 



fractus, Scudder, 1868, Mem. Bost. Soc. 



Nat. Hist., vol. 2, p. 234, and Acad. 



Geol., p. 496, Coal Mea 

 mazonius, Zittel, 



1885, Handbuch 



der Pal., p. 730, 



Coal Meas. 

 sigillari^e, Dawson, 



1860, Quar. Jour. 



Geo. Soc., vol. 16, 



p. 271, Coal Meas. FIG. 1073. Xylobius 

 RfiidHpr siglllariae. a, Organ 

 M T5 V with palpus, pertain- 



Mem. cost, ing to the mouth, en- 



Soc. Nat. Hist., larged. 



vol. 2, p. 234, and Acad. Geol., p. 496, 



Coal Meas. 



CLASS INSECTA. 



INSECTS are possessed of head, thorax, and abdomen. Three pairs of legs and 

 one pair of antennae belong to them in their perfect state. They are the highest 

 and most complicated class of articulated animals, and abound almost everywhere. 

 No living order, in this class, is known from the Palaeozoic rocks. Indeed, the 

 fossils consist almost wholly of fragments of wings showing little else than neura- 

 tion ; but they have been studied by Scudder, until he has classified them into an 

 Order and Families, to the general satisfaction of entomologists, and all must 

 concede he has accomplished a very difficult task. The Order Palaeodictyoptera, 

 which includes the Orthopteroid and Hemipteroid Palaeodictyoptera, has been de- 

 fined as follows : Body generally elongated ; mouth parts variously developed ; 

 antennae filiform ; thoracic joints subequally developed ; legs moderately large ; meso 

 and metathoracic wings closely similar, equally membranous ; the six principal 

 veins always developed; the marginal simple, and forming the costal border; the 

 mediastinal generally simple or with superior branches only ; the other veins usu- 

 ally dichotomize ; stout and well defined cross veins rare ; membrane generally 

 reticulate ; wings in repose lying on the abdomen ; the anal area of hind wings, 

 though usually of great distal extension, never plaited, though sometimes broadly 

 folded; abdomen usually long and slender, the last joint often furnished with sim- 

 ple articulated appendages. 



ORDER PAL^ODICTYOPTERA. 



FAMILY GERARIID^E. Adiphlebia, Gerarus, Megathentomum, Polyernus. 



FAMILY HEMERISTID^E. Chrestotes, Hemeristia, Lithentomum. 



FAMILY HOMOTHETID.E. Anthracothremma, Cheliphlebia, Didymophleps, 



Encaenus, Genentomum, Genopteryx, Gerapompus, Homothetus. 

 FAMILY MYLACRID^E. Lithomylacris, Mylacris, Necymylacris, Paromylacris, 



Promylacris. 

 FAMILY PAL^OBLATTINID^S. Archymylacris, Etoblattina, Gerablattina, 



Oryctoblattina, Petrablattina. 



FAMILY PAL^OPTERINID^. Aethophlebia, Dieconeura, Miamia, Propteticus. 

 FAMILY PALJEEPHEMERID.E. Ephemerites, Geraphemera, Platephemera. 



