842 



Pomona College Journal op Entomology 



The Colleml)ola were not widely distributed along the shore for they 

 were ioiind only on the rocks 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. Nowliere 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 the one family Entomobryida^ were found, and only two genera of 

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

 of which tlierc were fewer in luimbcr. 



Figure 268. Isotoma bidenticula Gntli. 

 Dorsal view. 



Isotoma bidenticula ((iuthrie) 



(Figures 207, 268 and 2(19) 



Fiuiiul uiidcr the largest rocks below the mean tide mark at hiw tide. 

 Length 1 Mini. Color — Dark, dull brown, mottled. Ventral side dark; light 

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

 sul)cylindrical ; sparsely haired. Head — Slightly elongate. Antenna^ (Figure 

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

 shortest, II longer than III, and IV longest, (iuthrie in his description of 

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

 I IoiiikI. Oci'Ui, sixteen. In each eye spot (Figure 269, D) there are two 

 w hiih are sinaller tiian the other six, i)robably showing degeneration. These are 

 ditferent in this respect tlum those described by Guthrie. The ocelli of his 

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

 — Tiie three segments not fused, eacii licar a ])air of legs that have five 

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

 tarsus very small and has two claws (Figure 269, A) without teeth; legs 

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

 Segments III and IV about equal in length; IV, V and VI fused so as to 

 almost ajipear as one. Furcida ( Figure 269, F) on penultimate segment ; short. 



