260 University of Calif ornia Puhlications in Zoology, [^ou 8 



eal distribution of the material, in which, however, the greater 

 part of the individuals are grouped about a mean. Thus five are 

 very small (22-40;li), G. catenata, palustris, scrippsae, series and 

 spinifera; four are small (40-60|U,), G. polyeeha, sphaeroidea, 

 triacaniha and turhynei; five are of medium size (60-80/u,), G. 

 alaskensis, apiculata, digitale, mihteri and polygramma; five are 

 large (80-lOOyu.), G. ceratocoroides, diegensis, fragilis and hya- 

 lina; four are very large (100-120/a), G. hirostris, glyptorhyn- 

 chus, htghleii, and kofoidi; and three are giants (130-250jli), G. 

 i)iffata, mitra and pacifica. 



In type of asexual reproduction two species exhibit very dis- 

 tinct features which set them off from all others. In G. catenata 

 Levander (1894:a) has described a type of chain formation with 

 accompanying skeletal fission, while in G. series I (1911a) have 

 found chain formation with accompanying reduction in size of 

 the terminal members of the series and what appears to be skele- 

 tal formation in entirety de novo after chain formation. In no 

 other species has chain formation been noted, though normal 

 binary fission of cell body and skeleton alike occur in a large 

 number and possibly in all of them. 



The distribution of the species is characteristic. Two only are 

 known from fresh water, G. apiculata and G. palustris; one, G. 

 catenata, from the brackish water of the Baltic, and one, G. tria- 

 cantha, appears to be a northern circumpolar neritic form. By 

 far the greater part of the species are primarily tropical or of the 

 warm temperate zone ; here belong G. hirostris, ceratocoroides, 

 fragilis, glyptorhynchus, highleii, hyalina, inflata, kofoidi, mil- 

 neri, mitra, pacifica, polygramma, sphaeroidea, and turhynei. 

 j\Iany of these invade temperate and even far northern or far 

 southern waters sparingly with currents from equatorial regions. 

 The species which appear to have a predominantly temperate 

 distribution are G. alaskensis, diegensis, digitale, polyedra, 

 scrippsae and spinifera, though these also invade tropical and 

 circumpolar regions to some extent. The marked increase in 

 speciation i)i waters of higher temperature is noteworthy. 



Nothing is known yet of their vertical distribution. 



The relative numbers in which the species occurs is also a 



