176 



THE MYRIAl'ODA OF NORTH AMERICA. 



The family character of this group which first attracts attention, is the large; number 

 of segments, each of which is composed of two unequal subsegments. The boundaries of 

 the respective scuta of each pair of the latter are well marked by sutures, &c, but the 

 sterna are completely consolidated. The head varies in form, size, &c, and furnishes the 

 principal generic characters. The number of joints of the antennae is fixed for the family, 

 but nevertheless good specific, and even generic, characters, arc derivable from these 

 organs. The most important specific characters besides those before alluded to are founded 

 upon, firstly, the peculiarities as to size, shape, proportion, &c, of the component portions 

 of the head and its appendages ; secondly, the color and form of the body, and the number 

 of segments composing it ; thirdly, the structure of the legs, especially of the last pair ; and, 

 finally, the markings and sutures of the scuta and sterna. I have never had an opportu- 

 nity of examining very large suites of specimens, so as to determine positively the con- 

 stancy of the various characters enumerated, but they probably do not vary a great deal. 



Gen. 1. MECISTOCEITIALITS, Newp.* 



Segmentnm cephalicom elongatum, aogustura, latitodine plus duplo longius. Antennae approximata), articulis 

 obconiois. Subsegmentum prebasale sejunctuin sod basale subbasaleque ooalita. Mandibulce magnae, intus den- 

 ticulate. (Fig. 18.) 



Cephalic segment elongate, narrow, more than twice as long as broad. Antennas approximate; articles obeonic. 

 Prebasal subsegment separate, but the basal and subbasal coalescent. Mandibles large, within denticulate. 



M. FULVUS. 



M. fulvus, politus; capite dilute aurantiaco, punctato, pilis longis rigidis paucis ; segnienfo oephalioo antice 

 truncato, postice illieo angustato ct vix truncato; antennis longis, pilis longis rigidis niultis; lubio 

 profunde punctato, antice emarginato, medio sulco impresso; mandibulis distinote punctatis, pilis 

 rigidis paucis, quadridentatis ; segmento anali piloso ; pedibus pilis longis, paribus , r )7. 



Fulvous, polished; head light orange, punctate, with a few long rigid hairs; cephalic segment 

 anteriorly truncate ; posteriorly rapidly narrowed and scarcely truncate; antennas with many lung 

 rigid hairs; labium profoundly punctate, anteriorly emarginato, impressed with a median sulcus; 

 \ mandibles distinctly punctate, with a few rigid hairs, quadridentate ; anal .segment pilose; feet with 

 long hairs, 57 pairs. 



M. fulvus, Wood, Journ. A. N. S., new series, 18G3, vol. v, p. 41. 

 ? Okophilus attenuates, S'iy, Journ. A. N. 8., 1st series, vol. ii. 



The cephalic segment is scarcely narrowed at all, except at the posterior end, where it 

 is rapidly contracted, being indeed rounded off. The body is slender and polished. The 



* Proc. Zool. Society, December, 1842, p. 179. 



