46 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
there is no definite line of division to separate these two parts, as is 
the case in Boettcheria and usually in Sarcophaga. The distal por- 
tion bears various processes, but no attempt has been made to define 
these. Those who desire to go more fully into the details of construc- 
tion are referred to Bottcher's paper (see Introduction). 
Chaetotaxy. 
Head. — The arrangement of the frontal bristles is more useful as a 
generic than as a specific character. In Ravinia the two rows are 
either parallel or their lower portions diverge slightly toward the eye 
orbits and scarcely descend below the base of the vitta. This is most 
pronounced in the females, but is distinct in both sexes, especially in 
the second group of the genus as later described. One American Sarco- 
phaga has the rows similarly arranged, also species of the assidua 
group (Sarcophaga), though the effect is less marked. Most Sarco- 
phaga and all species of Boettcheria have the rows extending well 
below the base of the vitta and their lower portions more or less widely 
divergent. The length and stoutness of the bristles decrease upward 
except in the uppermost pair or pairs which are longer and stronger 
than those immediately beneath. A line connecting the uppermost 
pair would pass through or just beneath the anterior ocellus in most 
species, but sometimes a wider space intervenes. In Blaesoxiphella 
of Villeneuve the frontal bristles diminish successively in length, dis- 
appearing entirely at the top of the ' frontal band ' (probably at apex 
of ocellar triangle). The vertical bristles are very stout and promi- 
nent. Their bases usually lie in the same straight line with those of 
the corresponding last frontal and occipito-central. Orbital and 
lateral vertical bristles are most commonly found in females, though 
sometimes in males. Species of certain genera have them in both 
sexes. The lateral verticals are unusually well developed in both 
male and female of a certain American Sarcophaga. Orbital bristles 
in the male are probably variable and not altogether reliable as specific 
characters. The vibrissae may be either on a line with or slightly 
or considerably above the oral margin. 
Thorax. — Anterior dorsocentrals are absent in one undescribed 
American species of Sarcophaga, a condition occurring most frequently 
among a certain group of tropical species, but are present in all others 
described. They may be approximately equal in length to that ot 
the vestiture of the prescutum or at least short and more strongly 
