172 CALIFORNIA ACADEMY OF SCIENCES. 



Sira Lbk. forms clothed with scales but with the meso- 

 notum not projecting. In consequence of this, the two 

 temporary genera Drepanura and Pseudosira, before pro- 

 posed by me, are to be excluded from the system. 



Gen. I. Tomocerus Nicolet. 

 Tomocerus americanus n. sp. 



The dental spines are 9-1 1 ', the two upper and the two 

 lower of which are considerably longer than the others. 

 The upper claw is provided with three or four teeth. The 

 lower claw is lanceolate and provided zvith one tooth. 

 Length 4. mm. 



As to the disposition of the dental spines of the caudal 

 appendage, the above species is closely allied to T. fav- 

 esecens Tullb. A pointed scale near the inner spine is also 

 to be found. The number of the spines seems to vary 

 considerably. 



The variation is generally confined to the numbers 9-1 1. 

 Characteristic is the disposition of the two flank spines 

 in each end, considerably surpassing the others in length. 

 The upper claw of the first pair of extremities often has 

 four teeth, that of the other pair three. Also in this I 

 have thought to find variation. Thus I have found several 

 specimens on which all the pairs of extremities have had 

 the upper claw armed with three teeth. 



In my memoir on Californian Collembola I have men- 

 tioned a species of Tomocerus Lbk., which, on account 

 of the limited materials I then had, I was not able to 

 determine. A renewed study of my old preparation has 

 shown that the species in question is identical with the 

 one now described. 



Habitat. San Francisco. (Coll. G. Eisen.) 



