Vol. 3] Kofoid. — Species Characters in Triposolenia. 125 



the contents coming from the deeper levels since the net does not 

 filter on the descent and has its filtration efficiency reduced dur- 

 ing its ascent. The individuals of the various species of Tripo- 

 solenia have been found with a single exception only in the hauls 

 from below the surface, and principally in those from the 70-130 

 fathom levels. Frequently several species have been found in a 

 single catch. Kepresentatives of this genus are extensively dis- 

 tributed throughout the Eastern warm temperate and tropical 

 Pacific. It is not improbable that Schiitts' ('95) AmpJiisolenia 

 tripos {nomen nudum) from the Gulf Stream is a member of this 

 genus. The investigations of Cleve ( '01 and '02) and others have 

 shown the cosmopolitan nature of the distribution of the pelagic 

 Dinoflagellates. jNIy own observations on the plankton of the 

 Pacific confirm this view. Triposolenia is not a genus restricted 

 in its distribution and the species here described are not local 

 forms. They will be found, beyond question, widely distributed 

 in the warmer seas. Over against the possibility of barriers of 

 temperature separating them in their vertical distribution should 

 be placed the probability of some vertical movement as a result 

 of vertical currents (see Holway :05) and also as a result of 

 heliotropism, the latter varying with the amount of carbonic or 

 other acids in the water (Loeb :03). In any case the coincident 

 distribution of closely related species is a common feature among 

 the pelagic protozoa with which I am familiar, e.g., among the 

 Coccolithophorida, the Silicoflagellata, other Dinofiagellata, the 

 Radiolaria, and the Tintinnidae. That these primitive animals 

 should have attained so high a degree of specific differentiation 

 in the presence of so great environmental uniformity, in the 

 relative absence of barriers, is a fact of profound significance to 

 be taken into account in any discussion of the process of organic 

 evolution. 



Zoological Laboratorij, Uuivcrsitij of California, 

 October 3, 1906. 



