1 889. J Synopsis of the Families of Vertebrata. 851 
ENTEROPNEUSTA. 
But one order of this class is yet known. 
No appendages to the body except an oval 
mass extending in front of the head; Helminthophya. 
The order Helminthophya embraces^ but one family, the Bal- 
anoglossidai. 
UROCHORDA. 
There is but one class of Urochorda ; viz. : 
Not metameric ; a mantel covering the body ; respiration 
pharyngeal; heart distinct, saccular; Tunicata. 
TUNIC ATA. 
There are two orders of Tunicata. 
Inhalent and exhalent openings close together ; ali- 
mentary canal elongate ; Asciduz. 
Inhalent orifice and anus at opposite extremities ; ali- 
mentary canal crowded into a body termed a 
nucleus ; Thaliacea. 
To the AsciDi^E belong the families Appendiculariidae, Clavel- 
linidas, Ascidiidae, Botryllidae, Didemnidae, Polyclinidae, and Py- 
rosomids. To the Thaliacea are referred the families Salpidae 
and Doliolidae. 
CEPHALOCHORDA. 
The only class of the Cephalochcrda is the following : 
No mantel ; walls of the body muscular myotomes ; 
no jaws nor extremities ; pharyngeal walls fis- 
sured ; heart a longitudinal vessel, which gives 
off branchial vessels, which unite into an aorta ; 
a liver and vena cava present ; Acrania. 
Of the class ACRANIA but one order as yet know. 
Pharyngeal fissures enclosed externally by a fold of 
the integument, which encloses a chamber 
(atrium) which opens inferiorly; openings of 
alimentary canal at opposite extremities ; heart 
tubular ; Leptocardii. 
The only family of the Leptocardii is the Branchiostomidae. 
