FAMILY TROMBIDIIDAE 689 



2. Body but little longer than broad ; median plate longer than 



broad agilis. 



Body much longer than broad ; ventral plate about as broad 

 as long echidninus. 



Laelaps echidninus, Berlese. Dorsal surface of body almost completely 

 covered by scutum and armed with rows of long curved bristles, six 

 in front and eight behind ; there is also a longer pair near the front 

 margin and a few at the sides. The legs are stout and comparatively 

 short ; the tarsus is about twice as long as the preceding segment ; there 

 is a stout spine situated about the centre of each coxa. 



This species is common on Mus decumanus and other rats in many 

 parts of the world ; according to Miller it is the invertebrate host of 

 Leucocytogregarina muris in the United States. 



Laelaps agilis has been recorded from rats in Europe and Africa, and 

 L. stabularis is found on the brown rat in Italy. Doubtless there are 

 many more species yet to be described. 



The genus Myonyssus, Tiraboschi, contains one species, decumani, 

 from Italy, where it has been recorded from Mus decumanus. The 

 above key will help to distinguish it from Laelaps. 



Two other genera, Raillietia and Haemogamassus, of which very little is 

 known, are believed to be blood-sucking in habit. Raillietia auris, Leidy, 

 occurs in the ears of cattle in the United States. The species belonging 

 to Haemogamassus are found on moles in Europe and America. 



FAMILY TROMBIDIIDAE 



The mites of this family are characterized by the presence of an 

 accessory finger-like appendage to the palps. The body is usually 

 divided into two portions ; the cephalothorax bears the anterior pairs 

 of legs, the palps, mouth parts, and eyes ; the abdomen proper is usually 

 larger than the anterior part, and bears the two posterior legs. The last 

 segment of leg IV is not swollen, while that of leg I is enlarged. Most 

 of the species are of a red colour. Like the Gamasidae this family 

 contains a number of forms with very varied habits. Those which 

 come specially into prominence are the harvest mites, common in 

 most countries and known by various local names, though the species 

 have not as yet been properly differentiated on account of the difficulty 

 of following the complete life history. 



The adults of these harvest mites are mainly predaceous, but the 

 larvae, which, as the name implies, appear in the autumn, are parasitic, 

 and attack the skin of mammals and frequently of man. Their presence 

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