696 CLASS XI. 
in 62° N. Lat.!. They appear on the coasts, however, only rarely, 
but keep by preference in the open sea, far from the continent. 
Ascidians, as well compound as simple, occur in much higher lati- 
tudes ; Boltenia ovifera was discovered in Davis’s Straits at 69° 
N.1L., Synotcum turgens in Phipps’s voyage at the north coast of 
Spitzbergen. Species of all the forms, nay, even of most of the 
sub-genera, are found in the Mediterranean sea; the apparent pre- 
ponderance in number of species in this sea, above all others, may 
however be principally ascribed perhaps to this, that its productions 
have been more perseveringly investigated by numerous observers, 
than those of the other seas. 
1 In the autumn of 1839 in great numbers near the island Bremanger; Sars 
Fauna littoralis Norvegie. Christiana, 1846, folio, p. 63. 
