a slender stalk to the base of the envelope; loricas variously tapering 

 at the base in diflFerent species, with smooth or undulate margins; 

 arranged in forked chains, 1 or 2 cones fitting into the wide mouth 

 of the lorica below; envelope colorless or brownish, composed of 

 cellulose and silicon (?); protoplast with 1 or 2 plate-like, parietal 

 chromatophores which are yellow-brown, and 2 flagella of different 

 lengths attached apically; pigment-spot and 2 contractile vacuoles 

 in the anterior end; food reserve leucosin, usually in the form of a 

 single basal granule. 



See Ahlstrom (1937) for a critical study of American species of 

 Dinobryon. 



Key to the Species 



1. Cells solitary, epiphytic 2 



1. Cells adjoined to form arborescent colonies; free-swimming 3 



2. Lorica an elongate cone, 6-7 times longer 



than the maximum diameter D. calciformis 



2. Lorica fusiform, 2 times longer than 



the maximum diameter D. Tabellariae 



3. Colony widely diverging, spreading 4 



3. Colony with loricas mostly erect, or slightly divergent, 



long axes often nearly parallel, compactly arranged 6 



4. Margins of lorica smooth throughout ( but often with one 



angular protrusion near the base) D. cylindricum 



4. Margins of the lorica undulate throughout, 



or in the basal or anterior portion 5 



5. Upper portion of the lorica with undulate margins; mouth flaring 

 decidedly; the basal portion as long or longer 



than the anterior portion .. D. Vanhoeffenii 



5. Upper 'portion of the lorica not undulate, mouth slightly flaring, 

 the basal portion with undulations above the posterior cone- 

 shaped apex; basal portion shorter than the upper D. divergens 



6. Lorica conical with slightly diverging 



sides and flaring at the mouth D. sociale 



6. Lorica campanulate or semi-cylindrical in the upper portion 7 



7. Lorica distinctly campanulate but often with unsymmetrical 

 swellings at the base of the anterior portion D. sertularia 



7. Lorica cylindrical in the upper portion 8 



8. Lorica with margins undulate, often extended posteriorly into a 



long or short acute or subacute point D. havaricum 



8. Lorica with smooth margins; basal portion shorter 



than the anterior cylindrical portion D. sertularia 



Dinobryon bavarictim Imhof 1890, p. 484 

 PL 98, Fig. 6 



Closely arranged loricas in slightly diverging colonies, the loricas 

 elongate-conical, tapering posteriorly to a sharp point ( the length of 

 the posterior part varying greatly, sometimes forming a short, sharp 



[377] 



