EEPORT OX THE THXICATA. 
173 
The reproductive organs occupy the post-abdomen, the region of the body behind the 
in testinalloop, and also encroach upon the abdomen. The usual median membranous 
septum is present in the post-abdomen. The ova and the spermatic vesicles occur 
together, and tailed larvae were found in the peribranchial cavity of one Ascidiozooid. 
The larvae (see PL XXI Y. fig. 15) have two pigmented sense-organs placed far back in 
the body, and the tail has a very broad membranous margin. 
Atopogaster elongata, n. sp. (PI. XXI Y. figs. 1-8). 
The Colony is of an irregularly elongated form, attached by the one end, and more 
or less pointed at the other. It is usually somewhat compressed laterally, but may 
be almost cylindrical. The surface is uneven and moderately smooth. The general 
colour is a pale grey, but it varies in difierent specimens from brownish to almost 
white. 
The length is about 10 cm., the greatest breadth 2 ‘5 cm., and the thickness about 1 cm. 
The Ascidiozooids are small, and are arranged quite irregularly. They are very 
numerous, and their anterior ends are closely placed all over the outer surface. The 
usual length of the Ascidiozooid is about 4 mm., while the greatest width is 0‘4 mm. 
The body is not distinctly divided into regions. 
The Test is compact and firm, and almost Cjuite opaque. The matrix is homogeneous 
or very slightly fibrillated. The test cells are very numerous, and are generally of an 
elongated fusiform shape. There are no vessels and no bladder cells present in the test. 
The Mantle is moderately strong. The muscle bands run mainly in a longitudinal 
direction ; they are closely placed on the post-abdomen . 
The Branchial Sac is of small size and its walls are opaque. The transverse vessels 
are relatively large, while the stigmata are variable in size ; sometimes they are small and 
inconspicuous, while in other cases they are of moderate size. 
The Tentacles are fairly large ; they are closely placed and of different lengths. 
Locality. — Station 313, January 20, 1876; lat. 52° 20' S., long. 67° 39' W. ; 
depth, 55 fathoms; bottom, sand; bottom temperature, 4 7° ’8 F. 
A large number of specimens of this species were obtained by the trawl at Station 
313 in the, Strait of Magellan. They differ from one another considerably in shape and 
size (see PI. XXIY. figs. 1, 2, 3), but the colony is always of elongated form, attached 
by one end, and usually tapering slightly towards the other. In some cases the colony 
is twisted, the upper half or one-third being bent round so as to point towards the base 
of attachment (PI. XXIY. fig. 3). The colony apparently never branches. In some 
cases there is considerable lateral compression, the thickness being much less than 
the breadth, but in other cases (or even other parts of the same specimen) the shape is 
