314 Illinois State Laboratory of Isatural History. 



One is near the edge of the fundus, and the other two are 

 placed one at each side of the shell a little above the 

 neck. Although the shell itself varies greatly in outline 

 and is asymmetrical, these tubercles are constant and 

 afford an easy means of recognizing the species. The 

 pseudopodia are simple and few in number. Length .143 

 mm.; width .111 mm. 



This species was found in towings taken in ISIatanzas 

 Lake during August. It was not common, and we 

 have seen it but once since. 



Ceratiuin hrevicorne n. sp. 



(Plate XXV.. Fis. 11 and 12; Plate XXVI., Fig. 13.) 



Body small, compressed, triangular; three spines, one 

 anterior and two posterior, the left posterior one quite 

 small. The surface is slightly roughened by the small 

 plates, but there are no small spines. The long anterior 

 spine smooth. 



This is a compact robust little species, about two and 

 a half times as long as wide. The shell is curved so as 

 to be convex on the dorsal surface and concave on the 

 ventral. The three horn-like processes or spines are 

 straight prolongations of the shell; no specimen was 

 found in which they were bent or curved. Length, in- 

 cluding spines, .115 mm.; width .046 mm. 



This is a rather rare form. It was found during Au- 

 gust in towings from Matanzas Lake, in company' with 

 Peridinium tabulatum Ehrbg., and has been observed 

 only at rare intervals since. It can be distinguished 

 very readily by its compact ti'iangular body and short 

 straight spines. 



Tintinnopsis illinoisensis n. sp. 



(Plate XXVI., FiK. H iind IC ) 



Animal small, ovate, inhabiting a narrow cylin- 

 drical or thimble-shaped chitinous shell, covered for 

 the most part with small sharp angled grains of sand. 

 Fundus obtusolv conical oi- rounded. Shell either of the 



