256 LIVERPOOL BIOLOGICAL SOCIETY. 
and on the North Spit, on July 24th, 1888. Alder gives the 
size as three-eighths of an inch. Most of the specimens 
at Puffin Island are rather smaller, about quarter of an inch 
to five-sixteenths in length, but I have one which measures 
even in the contracted state, fully half an inch (18 mm.) 
in its dorso-ventral extent. . 
The obliquity of the plane of attachment (Pl. XIIL., 
fig. 8, ad.) is a constant character, the flattened area being © 
not only more on the left side than on the right, but also 
more dorsally than ventrally so that the branchial aperture 
projects more freely than the atrial does. This appears to 
be solely a littoral species, as I have never taken it except 
between tide marks. It is found generally under large 
stones close to low water mark. In its external appearance 
from the absence of any coating of sand or shell fragments 
it is very unlike a Molgula, and has probably been often 
mistaken for the young of an “Ascidia, such as A. scabra. 
An examination of the apertures, however, shows at once 
that it belongs to the family Molgulide (Pl. XIIL., figs. 
7 and 8). 
As in the original account of this species only the 
external appearance is referred to, I shall add here the 
characters of the internal organs so as to complete the 
necessary description of the species :— 
The Test is thin, but cartilaginous like that of an Ascidia. 
It is semi-transparent, and has no encrusting sand. 
The Mantle is fairly muscular, but has none of the 
peculiar short fusiform muscle bundles usually found in the 
Molgulide, except to a slight extent at the sides of the 
endostyle. The branchial and atrial sphincters are very 
strong. 
The Branchial Sac has seven folds on each side. These 
are all much of the same size, and have three to five 
internal longitudinal bars each (Pik Salles fig. 9, br. fap iiine 
