194 



There is some tendency, especially in later years, toward the 

 colder months. Eight of the fifteen pulses occur below 70, and 

 twelve between September 1 and May 1 . 



On account of the small numbers the pulses are poorly defined 

 in our records (Table I.), but there are indications that they coincide 

 in location, in a general way, with those of other Brachionid<z and 

 the Ploima as a whole. They also in many instances coincide with 

 or follow shortly after the pulses of chlorophyll-bearing organisms, 

 as has been noted in other Brachionida. 



This species, B. urceolaris, is a cosmopolite, and of general occur- 

 rence in the fresh-water plankton of smaller and warmer bodies of 

 water. It is reported by Weber ('98) from Swiss marshes, by 

 Zacharias ('98) and Marsson ('00) from many smaller German 

 waters, and by Seligo ('00), throughout the year, from lakes near 

 Danzig, where it attains maxima in April, July, and September. 

 Since this author includes B. angularis (B. urceolaris forma angu- 

 latus Seligo) with his records of urceolaris, it is probable that the 

 species in the usual sense may have much more restricted numbers 

 and range in his region. Kertesz ('94) finds it about Budapest. 

 It is reported as sporadic in the vernal plankton of the Elbe by 

 Schorler ('00), and is listed from the Oder by Zimmer ('99). 

 Skorikow ('97) reports it once in summer plankton of the Udy 

 near Charkow. 



The species is exceedingly variable in the development of the 

 anterior spines, and in the proportions of the body. It varies 

 toward the bakeri group, and individuals are sometimes found which 

 seem to connect the two groups. I follow Skorikow ( '96) in placing 

 B. rubens as a variety of B. urceolaris, including in it those forms 

 whose anterior spines are least developed. The more slender 

 summer forms I have listed as var. bursarius Barrois and v. Daday. 

 From my observations on B. variabilis Hempel, I am inclined to 

 regard it as a possible variety in the urceolaris group. In form, 

 texture, proportions, and anterior spines it is certainly similar to 

 this group. The presence of the posterior spines would not suffice 

 to separate it, since these may or may not be present, and the 

 existence of a variety of urceolaris with such spines would only 

 present a phenomenon parallel to that observed in pala, angularis, 

 and bakeri. The quadrate foot-plate present in variabilis, which, 

 according to Hempel ('96), is not found in other species of the 



