ARACHNOIDEA. 575 



Note. Genus Myzostoma LEUCK., containing species that live parasiti- 

 cally in Comatulce, allied, according to JOH. MUELLER, to theArctisci, ought 

 perhaps to be placed amongst the parasitic Crustacea. See below. 



Section II. Holothoraca. Cephalothorax undivided. Organs 

 ispiration in most internal, distinct, with two or more stigmata 

 in abdomen, serving for the inspiration of air. 



A. Tracheae the sole instruments of respiration. 



ORDER III. Acarina. 



Cephalothorax conjoined with abdomen not divided into seg- 

 ments. Mouth in many in the form of a rostellum. 



Family III. Acarea. Head terminated anteriorly by labium 

 emarginate, or by a single bifid process. Palps connate with labium, 

 little distinct. Mandibles chelate. Ocelli none distinct. Feet 

 mostly terminated by an adhesive vesicle or acetabulum and claws. 



Compare on this family and the whole order A. DUGES Reclierches sur 

 VOrdre des Acariens, Ann. des Sc. nat., sec. SeVie, I. Zool. pp. i 40, pp. 

 144 174; II. pp. 19 63; which author we shall principally follow here, 

 for want of observations of our own ; also DUJARDIN sur les A cariens, in 

 Comptes rend. T. xix. p. 1158, and Ann. des Sc. nat. 1845, sec - SeVie, 

 Tom. III. p. 5 ; NICOLET Hist. nat. des Acariens qui se trouvent aux environs 

 de Paris, Archives du Mus. T. vn. 1855, pp. 381 482. 



Acarus LATR. Tyroglyphus (LATR. formerly), GERV. Body 

 Livided by a transverse furrow between the second and third pairs 

 i of feet. Four feet approximate at the insertion. 



Sp. Acarus domesticus DE GEEE, Acarus siro L. (in part), BERING, DE 

 GEER, Mem. vn. PI. 5, figs, i n, LTONET Kecherches, PI. 14, fig. 15, 

 DUMERIL Cons. gen. s. L Ins. PI. 52, figs. 4 7 (under the wrong name of 

 sarcopte de la gale ;) this small mite, living on old cheese, has in the young 

 state, like many Acarida, only six feet. 



Myobia V. HEYDEN. 



Sp. Sarcoptes musculinus KOCH, HERRICH-SCH^FFER Deutschl. Ins. Heft 138, 

 Tab. 13. 



Hypopus DUGES. 



See DUJARDIN, Mem. s. des Acariens sans bouche dont on a fait Ic genre 

 Hypopus, et qui sont le premier age des Gamases, in Ann. des Sc. not., 36 

 Serie, Zool. Tom. xu. 1849, PP- 2 45> 2 5- 



