of Edinburgh, Session 1879 - 80 . 
459 
majority of cases, to break down in regard to a few species. Tor 
example, Ascidia involuta has the entire body encrusted with sand 
grains and shells, a condition characteristic of the Molgulid^e ; simple 
unbranched tentacles, an important character in the Ascidiad.® are 
also found in Styela (Cynthiad^i); lastly, the papillated branchial 
sac of the Ascjdiad.® can no longer be considered an essential, 
Abyssascidia n. gen., having no papillae on its longitudinal bars. 
The more important characteristics of the AscmiADiE are the 
following : — 
Body sessile, attached. 
Branchial aperture eight-lobed, atrial six-lobed. 
Test gelatinous or cartilaginous. 
Branchial sac not conspicuously folded ; papillated. 
Tentacles unbranched, filiform. 
The family includes five known genera, two of which — Rhopalcea 
and Rliodosoma — are not represented in the “ Challenger ” collection, 
which however includes a new genus — Abyssascidia , and a new sub- 
genus of Ascidia — Pachychlaina. 
The “ Challenger ” Ascidiadze are divided into the following 
genera : — 
(1.) Ciona , Fleming, 1 species. 
(2.) Ascidia ., Linn., 8 species. 
Pachychlcena , n. sub-gen., 3 species. 
(3.) Abyssascidia, n. gen., 1 species. 
(4.) Corella , Hancock, 1 species. 
Of these fourteen species, twelve are new to science. The majority 
of the specimens are from shallow water (10 to 100 fathoms) ; two 
(. Ascidia tenera and Ascidia meridionalis) are from moderate depths 
(245 and 600 fathoms) ; while one ( Abyssascidia wyvillii) was 
obtained at the great depth of 2600 fathoms. 
The following table * shows the different genera and species 
eynoptically, and gives a few of their more important distinctive 
characters. 
* On account of the meagre, and in some cases insufficient, manner in 
which ascidians have often been described, it has been found impossible to 
extend the table so as to include the species already known. 
3 K 
VOL X. 
