228 BR. JOHNSTON ON THE ACARIDES OP BERWICKSHIRE. 



rounded, the back divided into a few large compartments, 

 separated by a mesial line, the tail-part depressed, angulated 

 and pointed, with a few hairs on the margin : Rostrum long, 

 tapered, porrect, declivous, surrounded with a collar at the 

 base, sparingly hirsute, but naked towards the apex : Palpi 

 (fig. 6.) originating in a little bulb from the collar of the 

 rostrum, pediform, slenderer and shorter than the legs, longer 

 than the rostrum, 4-jointed ; the 1st joint narrow at its ori- 

 gin but gradually thickening outwards, 2d joint cylindri- 

 cal, and as long as the first, 3d about one-half the length of 

 the second, the 4th as long as the second and third together, 

 more slender, cylindrical, furnished with a few long bristles ; 

 (no claw) : Legs 8, (fig. c.) alike, filiform, equidistant, nearly 

 equal in length, longer than the body, bristly, 5-jointed ; the 

 femoral joint elongate, thickening outwards, naked ; the 2d 

 and 3d short, the 4th twice as long as the second, the 5th as 

 long as the fourth or longer, tapered, rather abruptly nar- 

 rowed near the distal end, and furnished beneath with three 

 or four pairs of neat semi-pectinate processes, one of the pairs 

 situated at the insertion with the tarsus : Tarsus 2-jointed, 

 short, terminated with a pair of sharp curved claws moving 

 in the same direction, and separated by a large brush-like 

 pulvillus. — Linnaeus remarks that the rostrum, antennae or 

 palpi, and the legs are paler than the body, but this is only 

 after death, for during life the mite is unicolorous. The 

 bristles are colourless and sharp. • 



This pretty Acarus is common on our shore, where it may 

 be seen, during the summer months, running quickly amongst 

 stones and over the rocks above high-water mark. In shape 

 and size it is like an Apion. The rostrum consists of a cen- 

 tral conical tube, encased by a bivalvular sheath (fig. a), 

 the blades of the sheath lying parallel to the proboscis and 

 reaching beyond its extremity, where they meet. The apex 

 of the blades is cut into two clawlike denticles. Presuming 

 that the mite is insectivorous and suctorial, we may suppose 

 that the use of this cleft structure is to enable the animal to 

 hold its prey, while the proboscis is applied to its proper office. 

 It is difficult to assign the purpose of the elongation of the 

 palpi ; and we are equally at a loss to conjecture the use of 

 the semi-pectinate processes on the plantar edge of the lower 

 joints of the feet. 



The description in the Fauna Suecica leaves no doubt in 

 my mind that this is the species Linnaeus had then in view ; 



