842 



Pomona College Jottrnal op Entomology 



The Colluiiihola wltc not widely distributed along the shore for they 

 were found only on the roeks of one eove. Farther up the coast the majority 

 of the rocks were immovable, and on those that could be overturned, prac- 

 tically no specimens were found. Nowhere did they appear in any very 

 great abundance. They were all very small, less in size than those found on 

 land. As far as the specimens have been determined, the representatives of 

 only tlie one family Entomobryida? were found, and only two genera of 

 these, Entomohrya and Isntotna. This paper is concerned only with the last 

 of which there were fewer in number. 



^«%^?iV.'s''»5&ft^ 



Figure 268. Isotoma bidenticula Guth. 

 Dorsal view. 



Isotoma bidenticula (Guthrie) 



(Figures 267, 268 and 269) 



Found under the largest rocks below the mean tide mark at low tide. 

 Length 1 mm. Color — Dark, dull brown, mottled. Ventral side dark; liglit 

 at the junction of body segments; furcula and legs light. Body — Long, 

 subcylindrical ; sparsely haired. Read — Slightlj' elongate. Antennse (Figure 

 269, C) short, little longer than head; segments four, stout and rounded. I 

 shortest, II longer than III, and IV longest. Guthrie in his description of 

 this species states that III is longer than II, but this is not so with those that 

 I found. Ocelli, si.xteen. In each eye spot (Figure 269, D) there are two 

 which are smaller than the other six, probably showing degeneration. These are 

 different in this respect than those described by Guthrie. The ocelli of his 

 are all the same size. Post-antennal organ (Figure 269, E) is present. Thorax 

 — The three segments not fused, each bear a pair of legs that have five 

 joints; short coxa and trochanter; femur much longer; tibia still longer; 

 tarsus very small and has two claws (I^'igure 269, A) without teeth; legs 

 short. Ventral tube on first segment; tenaculum on second. Abdomen — 

 Segments III and IV a))out equal in length ; IV, V and VI fused so as to 

 almost appear as one. Furcula (Figure 269, F) on penultimate segment ; short. 



