THE acari:na ok mites. 



45 



Family C^CULIDiE. 



A few mites of peculiar appearance, somewliat like Nothrus of the Oribatidae, but 

 structurally allied to Trombidium, constitute this family. They are rather large 

 mites, of somewhat rectangular shape, and of a leathery 

 texture; the legs are very rough, and the anterior pairs 

 provided with a row of long spines. They terminate in 

 two claws. The coxae are aiTanged close together in a 

 radiate fashion. The dorsum shows a transverse furrow, 

 indicating the separation of cephalothorax and abdomen. 

 The former is provided with a median shield, and from 

 each posterior side arises a pedicel bearing two eyes 

 similar to those of Trombidium. The abdomen is proAdded 

 with two or more shields, according to the species. The 

 ventral openings are very large and close together, each 

 closed by flaps or valves. The mouth parts are small 

 and obscure, but the palpus is stout, five jointed, the 

 first and third joints very small, the penultimate ending 

 in a curved spine, the last forming- a "thumb." The 

 mandibles are stout and terminate in a curved claw. 

 They are concealed in the large conical rostrum. The 

 species are brown in color. Very little is loio^vn regard- 

 ing their habits and nothing as to life history. They 

 occur in moss, among fallen leaves, or in moist places. 

 They move very slowly and feign death when disturbed. 

 But one genus, Caeculus, is known. Several species 

 occur sparingly in southern Europe and northern Africa. 

 Banks (tig. 71) was discovered by Hubbard in southern California 

 is found among decaying leaves in the Eastern States. 



Fig. 71. — Caeculus americanus. 

 (Author's illustration.) 



One, Caeculus americanus 

 and another 



Superfamily HYDRACHNOIDEA. 



Family HYDRACHNID^. 



Since 0. F. Miiller described the Danish species in 1781, the water mites have 

 attracted more attention and study than any other family of Acarina. A large num- 

 ber of important papers have been published, particularly on the European fauna, 

 and one number of "Das Tierreich" (fascicule 13) is devoted to them. The body la 

 commonly short, usually high, and sometimes nearly spherical. It is entire, there 

 being no division into cephalothorax and abdomen. The legs arise close together 

 on the anterior part of the venter, and often in a radiate arrangement. They have 

 one or two simple eyes each side; in some cases these are situate close to the median 

 line. In one group the two eyes each side are situate on a common chitinous plate 

 called the eye capsule. The tegument is often soft, but sometimes provided with 

 dorsal shields or covered with a pitted cuirass. The mouth parts are often hidden 

 under the anterior margin of the cephalothorax. The beak (rostrum or capitulum) 

 is usually elongate pyriform, and the mandibles are two-jointed, with a clawlike 

 terminal joint; sometimes they are elongated into needlelike piercing organs. The 

 palpi (maxillary) are of four or five joints, the basal one often very small, the apical 

 one sometimes folding against the penultimate. The palpi vary greatly in shape, 

 and are of great value in classification. The legs are usually of seven joints, rather 

 subequal in length, although the fourth pair is commonly the longest. The coxse 

 are often broad and entirely united to the venter, and frequently to each other, thus 

 forming coxal or epiineral plates — sometimes four, sometines three, and in a few 

 genera united into one plate. The tarsi often terminate broadly, usually have two 

 claws, and are pro\'ided with hairs and bristles. Sometimes there are rows or tufts 



