290 Illinois State Laboratory of Natural History. 



XXXVI., Fig. 4). In the subsequent stages this mass assumes 

 a yellow and then a brownish color, takes on an irregular shape 

 (PI. XXXVI., Fig. 5), and disintegrates, leaving the empty cell 

 walls occupying the matrix. In spite of the suggestion in the 

 above description there was never any trace of the formation 

 of spermatozoa in the colonies presenting these phenomena, 

 neither was there any indication of encystment. There was 

 no indication of either a fungous or an algal parasite, and it 

 seems not improbable that the occurrence of these diseased 

 forms may have been due to some unfavorable local condition 

 in the water tributary to the habitat of the genera affected. 



The following brief synopsis of the prominent characters 

 of this genus and its two species will serve as a convenient 

 diagnosis for their determination. 



Pleodorina Shaw. — Colony consists of a spherical or ellip- 

 tical coenobium of greenish biflagellate cells of two types, 

 vegetative and gonidial, in the anterior and posterior parts 

 of the colony respectively, which lie in the periphery of a 

 hyaline gelatinous matrix and are surrounded by a common 

 hyaline envelope. Cells each with one reddish stigma, which is 

 more prominent in the anterior part of the colony. No con- 

 necting filaments between the cells. Non-sexual reproduc- 

 tion by gonidia, which are formed by increase in size of a 

 part of the cells of the colony. Daughters escape from 

 parent as small colonies of biflagellate cells which at this 

 stage are all similar. Sexual reproduction not known. 



P. californica Shaw. — Number of cells in colony 64 or 128. 

 Maximum diameter of colony 175-340 //. Vegetative cells 

 constituting approximately one half the colony. Gonidial cells 

 2-3 times diameter of vegetative cells. Known habitat : ponds, 

 ditches, and streams in California, Indiana, and Illinois. 



V. illinoisensis n. sp. — Number of cells in colony usually 

 32, rarely 10 or 64. Dimensions of colony range from 

 46x38 H to 200x175 /<•. Vegetative cells always four in 

 number. Gonidial cells approximately 1.1 — 2 times diam- 

 eter of vegetative cells. Known habitat: submerged lands 

 along the Illinois Paver. Types deposited in collections of 

 Illinois State Laboratory of Natural History and United 

 States Nationn 1 Museum. 



Illinois Biological station. Havana, 111.. July 25, 1898. 



