84 TRANSACTIONS LIVERPOO! BIOLOGICAL SOCIETY. 
Family VII. Pouystyenin#:— Ascidiozooids not 
erouped in systems. JBranchial and atrial apertures 4- 
lobed. Branchial sac may be folded; internal longitudinal 
bars present. The chief genera are—Thylacwwm, with 
ascidiozooids projecting above general surface of colony; 
Goodsiria, with ascidiozooids completely imbedded in 
investing mass; and Chorizocormus, with ascidiozooids 
united in little groups, which are connected by stolons. 
The last genus contains one species, Ch. reticulatus, a 
transition form between the other Polystyelide and the 
Cynthiide among Simple Ascidians. Thylaciwm is the 
only British form. 
Sub-order III. Asctpia Lucia. 
Free-swunming pelagic colonies having the form of a 
hollow cylinder closed at one end. The ascidiozooids 
forming the colony are imbedded in the common test in 
such a manner that the branchial apertures open on the 
outer surface, and the atrial apertures on the inner surface 
next to the central cavity of the colony. The ascidiozooids 
are produced by gemmation from a rudimentary larva (the 
cyathozooid) developed sexually. 
This sub-order includes a single family, the PYROSOMIDA, 
containing one well-marked genus, Pyrosoma, with several 
species. They are found swimming near the surface of 
the sea, chiefly in tropical latitudes, and are brilliantly 
phosphorescent. A fully developed colony may be from 
an inch or two to upwards of foar feet in length. Pyro- 
soma does not occur in British seas. 
