THE HABITS OF MONODONTOMERUS. 101 
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mid-day sun, sometimes to as much as 84° Fahr. at a depth of one inch and a half, as I 
have elsewhere shown*, and much of this heat is retained throughout the whole twenty- 
four hours; so that, in all probability, the growth of the pregnant Acari, and the hatching 
of their ova, then proceed very rapidly; while, on the contrary, these, as well as the 
changes of the bee-larvæ, are entirely arrested during winter. This will explain, what 
might otherwise seem to be discrepant, that some young Acari were produced after expo- 
sure to the sun, and in a warm room in October, while others not exposed to the sun, and 
the season becoming colder, have remained until the present time undeveloped. 
Having stated thus much respecting the economy of this microscopic parasite, I will 
now endeavour to describe it, and to show that it constitutes a new genus of its class. It 
belongs to the section Tyroglyphus of Latreille and Gervais, the tribe Sarcoptides of Koch, 
whieh has the Sarcoptes scabiei of the human subject as its type, and which includes also 
the Demodez folliculorum of Simon and Owen, a parasite in the follicles of the hairs in 
Man. It is most nearly allied to Koch's genus Dermaleichus, most of the species of which 
are parasites on birds; but it is perfectly distinct from that, as well as from the genus 
Trichodactylus of Dufour, a parasite on the Mason-bees of the genus Osmia. It is equally 
distinet from the Ansetus of Dujardin, which also is a parasite on bees, although it 
approaches these two genera in certain particulars. It resembles the latter in the general 
elongated form of body and in the size of the haunches of the legs; but it differs in the 
body being articulated throughout, in having a somewhat cordiform moveable head, the 
prothorax distinct from the trunk and abdomen, and the anterior pair of legs palpiform, 
while the three posterior pairs are equal, and terminated by four-jointed slender tarsi, the 
last joint in each being cordiform and pad-like, as in the larva of Stylops. In this latter 
respect it has affinity with the genus Hypopus of Dugès, as it has also with Trichodac- 
tylus in the legs being covered with a few very long hairs. 
With regard to the change and enlargement of the body in the female sex of the Acarus, 
every one will remember that its parallels are to be found amongst true hexapods, in the 
Termites and the Pulex penetrans. 
The characters I would assign for the new Acarus are :— 
Class ACARI. 
Fam. SARCOPTIDES, Koch. 
Gen. HETEROPUS, Newp. 
Corpus elongatum, subarticulatum. Caput mobile. Thorac a trunco distinctus, ad latera 
corpusculis clavatis munitus. Pedes anteriores palpiformes ; reliqui (parium trium 
posteriorum) æquales, arcuati, attenuati, tarsis gracilibus 4-articulatis, articulo 
terminali lato vesiculari. 
H. Lyris (figs. 6, 7 & 8), pallid® ferrugineus, capite saturatiore, prothorace paribus 
2 pilorum longorum, pedibus subrobustis; articulis omnibus long? pilosis: tibiæ 
articulo apicali corporis dimidium æquante. — Long. 4—1 lin. 
g gravidæ abdomine magnoperè inflato vesiculari. 
— Hab. in nidis Anthophore retuse, apud Gravesend, in comitatu Kent, mense Sept. 1849. 
* Phil. Trans. 1837, p. 279. 
VOL. XXI. 
