NO. I BLACK FLIES OF GUATEMALA — DALMAT 169 



Head: Light orange brown. Design on frons-clypeus (pi. 40, 

 fi&- 37'^) dark brown, composed of 4 elongated patches in form of 

 cross ; epicranial plate of each side with approximately 6 darkened 

 patches, the arrangement of these shown on plate 40, figure 371. Each 

 cephalic fan with 51-55 pectinate branches, the fine hairs on these 

 rather close, simple, long, accentuated at regular intervals by some- 

 what longer, stouter hairs. Mandible with 2 broad flattened teeth on 

 its inner margin, the more-distal longer and rounded at apex ; more- 

 proximal tooth about one-third the length of distal and more pointed 

 than it ; at times, only the longer tooth is present. Antenna 450 [i 

 long, light brown to yellow ; 4-segmented, the second segment with 

 2-3 superficial indentations appearing to divide it into 3-4 parts ; seg- 

 ments I, 2, and half of 3 reaching the apex of stalk of cephalic fan. 

 Submentum with 9 apical teeth, the median one and the two external 

 ones longer than the others ; teeth triangular in shape, pointed ; ventro- 

 lateral row irregular, composed of 9-1 1 stout hairs, the three most 

 apical ones trifid, the fourth bifid, and the others bifid or simple ; 

 lateral margin of submentum with 6 teeth in regular order. Occipital 

 cleft, triangular in shape (pi. 42, fig. 408). 



Thorax and Abdomen : Pseudopod (thoracic proleg) with 50- 

 60 rows of hooks at its apex ; postclypeal sclerites small, heavily sclero- 

 tized, well separated from each other. Posterior sucker with 350-360 

 rows of hooks. Anal gills composed of 3 main branches, each with 12 

 fingerlike projections, some shorter than others, the entire middle 

 group somewhat longer than the others. The X-shaped sclerite is 

 simple, well sclerotized, without pigmented patches ; no rectal scales 

 or spines, but with very small tuberculated hairs sparsely distributed 

 between anterior and posterior arms of each side. No ventral papillae 

 or sclerotized plaques on the eighth segment. 



Remarks. — Shnnlium (D.) acatcnangocnsis appears quite similar to 

 5*. {D.) vtrgatum Coq. (Coquillett, 1902; Stone, 1948), 6^. (D.) rubi- 

 cundnlum Knab (Vargas, 1942), and S. (D.) mafhesoni Vargas 

 (1943). It can be readily distinguished from vtrgatum as follows: 

 The abdomen of the female virgatmn is light brown with all the seg- 

 ments at least partially gray-pruinose above, while that of acatcnango- 

 ensis is black with only the tergites of the first two segments bearing 

 white pruinosity. The apical angle of the expansion of the genital fork 

 of acatenangoensis is more acute and much more heavily sclerotized 

 than in virgatmn. The outer basal angle of the former is more elongate 

 with the tip blunt. The base color of the abdomen of the male 

 acatenangoensis is completely black and the sternites are light brown 

 with a median, longitudinal black band, while the abdomen of virgatum 



