upon characteristics of the test rather than on those of the proto- 

 plast. The test is brown, often opaque, or tan to nearly colorless, 

 according to the amount of iron compounds deposited in it. The 

 test may be smooth or decorated with spines, warts, reticulations, 

 punctations, or combinations of these. The protoplast inside is highly 

 metabolic and has the general features of the euglenoids. There is 

 1 flagellum, a red pigment-spot, and numerous ovoid, disc-like 

 chloroplasts which may have pyrenoids. Reproduction is by cell 

 division, which takes place within the test, one of the new cells 

 escaping through the aperture and secreting its own shell. 



Although a few species may appear in the euplankton, most 

 species of Trachelomonas occur in shallow water of swamps, ditches, 

 and lagoons as tychoplankters, especially where there is a high con- 

 centration of organic matter and where temperatures are high. The 

 organisms may be so abundant as to color the water brown, although 

 they never form a conspicuous surface film as does Euglena. 



Key to the Species 



1. Test with the flagellum opening in a neck, or 



surrounded by a collar 2 



1. Test without a neck or collar around the flagellum aperture 22 



2. Flagellum opening in a distinct neck 3 



2. Flagellum opening in a collar or thickened ring (*) 12 



3. Test globose, with 4 or 5 long, sharp spines T. aculeata 



3. Test with shorter, more numerous spines 4 



4. Test extended into a long, spine-tipped caudus T. speciosa 



4. Test without a caudus, or if present not spine-tipped 5 



5. Test sexangular-ellipsoid T. hexangulata 



5. Test some other shape 6 



6. Test broadly ovoid, wrinkled and rugose; 



neck twisted or curved T. scabra 



6. Test shaped otherwise; not rugose' 7 



7. Test rectangular-fusiform, margins retuse, extended into a 



caudus T. Girardiana 



7. Test some other shape, not extended into a caudus 8 



8. Test elongate-ellipsoid 9 



8. Test oblong-cylindric or oblong 10 



9. Test with numerous, minute spines, punctate; 



margin of collar smooth T. bulla 



9, Test with scattered, stout spines; collar 



toothed at the margin T. sydneyensis 



10. Test oval to oblong, collar curved T. similis 



10. Test some other shape; collar not curved 11 



( * ) The thickened ring is a variable feature in some species. For question- 

 able forms, follow through both No. 2 choices. 



[408] 



