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and some are so closely related that it is not easy to identify them. 

 Of the eight species recorded from rats, four have been taken in this 

 country. It is not practicable to tabulate these eight species, but 

 the four that occur in our country may be arranged as follows: 



1. Hind tarsal joint II with an apical spine much longer than joint III acutus. 



Hind tarsal joint II with spines not longer than joint III 2 



2. Pronotal comb of about 26 spines . tiiger. 



Pronotal comb of about 18 or 20 spines fasciatus and londinensis. 



CeratopJiyllus niger Fox. 



This species has the pronotal ctenidia of about 26 spines; there 

 are a few hairs on the inner surface of hind femur; apical spines of 

 second joint of hind tarsus not longer than third joint; three hairs 

 in front of the eye and three in front of these; movable finger of claspers 

 with five slender bristles on the outer edge. Color, very dark brown. 

 Length 3.5 millimeters. 



Taken in California from Mus decumans and from man. 

 CeratopJiyllus acutus Baker. 



This species is readily known by having a spine at tip of the second 

 joint of hind tarsus longer than the third joint and reaching over 

 onto the fourth joint; the abdominal tergites have each two rows of 

 bristles; the male claspers are very large and long, sickle shaped. 

 Color, pale brown. Length, 3 to 3.5 millimeters. 



It was described from a spermophile, but Doctor Fox has taken it 

 once from a rat in California. 

 CeratopJiyllus fasciatus Bosc. 



There are 18 or 20 spines in the pronotal comb; there are three 

 bristles in front of eye and in female two, and in male four in front 

 of these ; there are three or four hairs on the inner surface of the hind 

 femur ; the proportions of joints in the hind tarsus are 50-33-20-1 1-21 . 

 The manubrium of the male claspers is very long and slender, and 

 some of the bristles on the movable finger are as long as the joint. 

 Length, male, 1.8 millimeters; female, 2.5 millimeters. 



It has been recorded from California on rats, mice, skunks, and 

 man. It is also common in Europe and elsewhere on rats, mice, and 

 other small animals. 

 CeratopJiyllus londinensis Rothschild. 



This is allied closely to C. fasciatus, and is best separated from that 

 species by the shape and armature of the genital parts; the manu- 

 brium is not as long as in that species, and the bristles on the movable 

 finger are shorter; the third joint of the maxillary palpi is propor- 

 tionally longer than in C. fasciatus. There are three bristles in front 

 of the eyes and four or five in front of these; there are a few hairs 

 on the inner surface of the hind femur; the proportions of the joints 

 in the hind tarsus are 46-30-18-11-18. 



