DETERMINATION OF SPECIMENS. 55 



ff Animals bag-shaped, with in- 

 current and excurrent orifices, 

 of which the latter may be held 

 in common by the colony. 

 Arrangement of animals in 

 rows, rosettes, bunches, etc. 

 All marine. 



Ascidiacea, sub Prevertebrata. 

 ** Free-swimming, all marine. 



f Colonies cylindrical or conical, 

 with one end open; separate 

 animals tubular, with an open- 

 ing at either end. 

 Ascidiacea, sub Prevertebrata. 



f f Colonies chain-like, in single or 

 double rows; separate animals 

 cask-shaped, with zone-like 

 bands; transparent. 

 Thaliacea, sub Prevertebrata. 

 {h) Solitary, or, if associated, without organic con- 

 tinuity. 



* Sessile, aquatic. 



f With two calcareous shells, dorsal 

 and ventral. Two spiral, cili- 

 ated arms supported by skele- 

 ton within the shell. 



Brachiopoda, sub Vermes, 



ff With calcareous shells, but not 

 as above and without the spiral 

 arms Some Mollusca. 



f ff Microscopic forms in tubes. 

 Ciliated lobes at free end. 



Rotifer a, sub Vermes. 



tttt Bag-shaped, either with or 

 without a stem ; two openings, 

 incurrent and excurrent. 

 Ascidiacea, sub Prevertebrata. 



