40 



REPOET 108, U. S. DEPAETMEXT OF AGEICULTUEE. 



There are several genera in the family, but only four are so far known from the 

 United States. 



1. Legs I and II with stout spines, each metatarsus with two little raised disks 



Caeculisoma. 



Legs without spines and without disks 2 



2. Mouth parts retractile 3 



Mouth parts not retractile 4 



3. No crista; usually six eyes; palpi four-jointed Sniaris. 



Crista present; only four eyes; palpi five-jointed Fcssonia. 



4. Hind tarsi with plume of long hairs; two eyes each side on body Eatoniana. 



Hind tarsi without the plume \ 5 



5. A distinct suture between cephalothorax and the abdomen; but one eye 



each side Belaustium. 



No distinct suture 6 



6. Two eyes each side on body; legs IV very long Erythraeus. 



One eye each side; legs IV shorter Atomus. 



Thor, who has recently published on this and allied fami- 

 lies, makes Smaris (fig. 58) the type of a special family. 

 He finds that in this genus there are no spiracles near the 

 beak, as in other Prostigmata, and that there are no large 

 tracheal trunks in the body. There are a great many fine 

 tracheae in this mite, and Thor believes that respiration is 

 effected through the skin, the structure of which is rather 

 peculiar. Upon these differences he bases a family; how- 

 ever, in my opinion this is but more evidence (if such is 

 needed) of the uselessness of a classification based on the 

 respiratory system. 



In Smaris the mouth parts are retractile, and so are often 

 invisible; the palpi are four-jointed and there is conunonly 

 an extra pair of eyes near the anterior margin, making 

 six in all. These median eyelike spots are, perhaps, 

 not true eyes but homologous with the crista metopica of 

 Erythraeus. 



In Fessonia the mouth parts are less retractile than in 

 Smaris, and there are but four eyes. The palpi are five- 

 jointed and the dorsal groove is sometimes swollen in the 

 middle. 



In Erythraeus the mandibles are retractile, there are but 

 four eyes, and the palpi are five-jointed. We have many 

 species of this genus, and several of them are common 

 and widely distributed. They are predaecous and suck 

 the juices from any small insect that they are able to 

 catch. One species has been found preying on the gloomy 

 scale (Chrysomphalus tenebricosus Comst.) and others are found feeding on the San 

 Jos6 scale and other scale insects. In this situation they are often the proy of 

 aphLs lions (Chrysopa). 



The larva that in Europe occurs commonly on ])halangids and which was described 

 by Oudemans as a new species (E. ignotus) has been shown by Evans and by Bruyant 

 to be that of E. nemorurn Koch. In this country we also have a species whose lar\-a 

 is frequently attached to daddy-long-legs, but it has not been connected with the 

 adult form. The generic name Erythraeus was formerly applied to a mite of another 

 family, but it is clear that its type species and original ai)plication bring it 

 into this family practically to replace Rhyncholophus} The genus Atomus Latreillc 

 was made for a larva of this family, the adult being congeneric with R. ncmorum. 



Fig. 57. — Erythraeus simplex 

 and palpus. (Author's il- 

 lustration.) 



1 liittcrla Kramer is not available, as the autlior neglected to place any species in it. 



