138 REPORT—1840. 
found in the mud-filled cavity of a dead bivalve, from thirty fathoms 
water, in the Frith of Forth ; two specimens of the other were dredged 
near Rothsay. 
The appearance of these animals was so peculiar, that the authors were 
unable to determine their position in the system, till anatomical exami- 
nation displayed their relation to the Tunicata, and revealed the inter- 
esting character of the genus to which they belong. 
The animals of this genus are free, elongated, dilated posteriorly, 
with the respiratory and excretory orifices approximated, the first being 
at the anterior end, in the axis of the animal. 
As both the species were found in muddy ground, the genus is 
named Pelonaia (xnhos vaw). 
The Frith of Forth species, P.corrugata, is characterized by trans- 
verse, somewhat irregular rug; dark brown; length 24 inches. 
The other species, P. glabra, smooth, with slight villosity ; grayish- 
white; length 1 inch. 
The author found the two species to possess the general structure of 
the other Ascidians. The peculiarities were—1l. The respiratory open- 
ing has no radiated folds or papillary fringes. 2. The respiratory sac 
is elongated, median, exhibits transverse folds, which contain the 
primary branches of the branchial artery and vein, and are tied to the 
internal surface of the muscular sac, and to the reproductive tubes, by 
a longitudinal row of thread-like bands on each side. It gradually 
contracts posteriorly into the cesophagus. 3. The digestive tube 
floats free in the capacious cavity of the muscular sac, except where it 
is tied down by vascular bands, and it terminates in free, floating, and 
radiating extremities in the interior, and half the length of the animal 
from the excretory opening of the sac just mentioned. 4. The vascular 
system exhibits no heart; and in consequence of the peculiar relative 
position of the respiratory sac and the other viscera, the system is 
symmetrical, the blood flowing backwards in the branchial vein and 
systemic artery, and forwards in the systemic vein and branchial 
artery, these two systems forming a dorsal and ventral trunk. 5. The 
reproductive organs consist of two elongated tubes, shut at one extre- 
mity, opening at the other into the cavity of the muscular sac, and 
closely attached to its inner surface. The orifices of these tubes are 
situated at the anterior third of the animal, and one-third of the poste- 
rior extremity of each is turned inward and forward, so as to become 
parallel to the rest of the tubes and to the branchial artery. Along 
the whole length of these tubes, close-set parallel czeca open into their 
cavities, a simple form, in fact, of the more complicated reproductive 
organs in the other Ascidian genera. 6. The principal peculiarity of 
the muscular cloak is firm adhesion to the whole internal surface of 
the tunic. In consequence also of the attachment of the viscera to 
its internal surface along the lateral lines only, its cavity is made more 
capacious, resembling, in this respect, the water-filled cavity of certain 
Echinodermata. A strong band is situated just behind the excretory 
orifices. 
From what has now been stated, it appears that external and internal 
