NORTH AMERICAN SPRING-TAILS— FOLSOM, 



453 



tibia and two tarsal segments — a primitive condition normal in 

 Pauropus and Polydesmus. In Tomocerus, as in other Collembola, 



3 4 



Fig. 2.— Tomoceeus flavescens, var. ameeicanus. The abdominal segments aee numbered, x 2Q 



two pre-coxal segments are present (fig. 2). These Willem ('00, 



p. 93) regards as equivalent to the two pre-coxal segments of the 



cockroach, that occur in 



^ other Orthoptera under va- 



rious modifications, as de- 

 scribed by Miall and Denny, 

 The structure of the claws 



of Tomocerus has been de- 



csribed minutely by Absolon 



('03). Some disagreement 



has existed in regard to the 



precise structure of the teeth 



of the unguis, which are of 



considerable phylogenetic 



importance. In a lateral 



view of the unguis a single 



series of teeth is seen, as in 



plate 40, figure 3. Willem 



('00, p. 45) maintained that 



these minute teeth are not 



single, but paired, the two 



teeth of each pair being side 



by side, and one hiding the 

 other in a lateral aspect of the claw. Borner ('01, p. 39) described 

 the unguis as being triangular in transverse section, with a simple, or 



Fig. 3.— Tomocerus 

 flavescens, vae. 

 ameeicanus. Ti- 

 biotarsus show- 

 inq an abnoemal 



THIED segment. 



X57. 



Fig. 4.— Tomocerus flavesCKns, 

 vae. ameeicanus. concave 



aspect of UNGXnS to SHOW 

 THE FORM OF THE TEIETH. X 644. 



