120 
Sarcoptes 
among the scales covering the notogaster that Railliet gave the name “clairiere” 
in distinction to “plastron,” by which he denotes what we call the plastron or 
rugose area. He remarks (1895, p. 641) with reference to S. scabiei Latr. that: 
“les ecailles dorsales, chez la femelle ovigere, tendent en general a s’atrophier 
sur deux points, en laissant vers la ligne mediane une clairiere plus ou moins 
nette; au niveau des epines posterieures du notothorax (clairiere anterieure), 
et au niveau des epines anterieures du notogastre (clairiere posterieure).” 
It is probably to these areas that Canestrini and Kramer refer when they 
define S. scabiei var. equi as having “eine vordere und eine hintere Riicken- 
blosse.” Warburton is, I believe, mistaken when he states that “clairiere,” 
“blosse,” and “plastron” have all been used for the same structure, the 
plastron on the notothorax. 
Behind the plastron on each side are three cones ( co ), (“notothoracic 
cones,” Munro, Warburton; “Schulterzapfen,” Canestrini and Kramer; 
“epines courts,” Railliet; “coni scapolari,” Canestrini). 
The antero-median cone lies behind the posterior angle of the plastron, 
the antero-lateral far out on the side of the body, and the posterior nearer 
the first than the second. The cone is considerably larger than the spine, acorn¬ 
shaped, covered at its base by one of the ordinary ridges of the integument, 
and articulated into a depression in the centre of an oval chitinous plate; 
this plate lies beneath the integument but is visible by reason of its brown 
colour. 
On each side of the posterior part of the body there are seven blunt, 
lancet-shaped spines ( sp ). They are arranged in two longitudinal rows, a 
straight median one of three spines, and a curved lateral of four. It is convenient 
to designate this arrangement as 3 : 4. The posterior spine of the lateral row 
is finer and shorter than the rest. The spines are essentially similar to the 
cones and differ only in being articulated to a round plate of chitin, which 
appears to lie in, not beneath, the integument. The cones and spines differ 
from the scales in that instead of being merely specialized portions of the 
integumentary ridges, they interrupt the ridges and arise from independent 
chitinous plates; they are possibly specialized setae, and a consideration of 
the chaetotaxy of allied genera might show whether this is so. 
The chaetotaxy is of systematic importance, and there is considerable 
disagreement between the figures of earlier writers; some of the smaller setae 
for long passed unnoticed, and not seldom ventral setae were observed by 
transparence and figured on both dorsal and ventral aspects. I have lettered 
every seta, and this will help with the comparative study of other species of 
the genus. Robin (1860) has already devoted attention to the comparative 
chaetotaxy. 
On the dorsal surface there is a pair of short thick bristles (D 1) arising 
from pits in the small shagreened area which lies just in front of the epistome. 
Behind the posterior angle of the plastron a pair of very long setae ( D'2) 
arise; these setae are directed outwards and forwards in the living mite when 
