REPORT ON THE TUNICATA. 265 



This table brings out very forcibly — first, the greal preponderance of Ascidians in 

 the southern over the northern hemisphere, there being about six times as many entri 

 on the right hand side of the table as on the left; and secondly, the atrandanee of 

 Tunicata in the far south, the two last divisions on the right hand side (30° to 40° and 

 40° to 55°) 25° in all, containing each of them more entries than all the other divisions, 

 both north and south latitude, taken together. 



Consequently, it appears from the Challenger investigations that Simple Ascidians are 

 not abundant in the northern hemisphere, and are comparatively scarce in tropical latitudes, 

 while they attain their greatest numerical development in southern temperate regions. 



Taking up particular groups of species, we find that the Challenger Molgulidae were 

 all obtained in the southern hemisphere, and between the latitudes of 30° and 55° S. 

 Two species of Molgula were found between 30° and 40° S., while all the rest, including 

 the genera Ascopera and Eugyra, and most of the species of Molgula, are from latitudes 

 between 40° and 55° S. 



The Cynthiidse range over both hemispheres, extending from between 40° and 45° 

 north latitude, to between 50° and 55° south latitude. The sub-family Bolteninse has 

 an equally extended range, but is most abundant in the far south. The number of 

 species found in the extreme right hand column (40° and 55° south latitude) equal 

 those in all the other columns put together. 



In the genus Boltenia, one species occurs in the extreme north, while the other two 

 are from far south, the genus being unrepresented in intermediate latitudes. 



The genus Culeolus has also a very considerable horizontal range, two of the species, 

 Culeolus murrayi and Culeolus perlatus, being found in the northern hemisphere, while 

 the remaining four are from the southern. Those in the northern seas are from the 

 temperate zone, while of the southern forms, one, Culeolus moseleyi, is from near the 

 equator ; one, Culeolus wyville-thomsom, from between 20° and 30° south latitude, and 

 the remaining two species are from much further south. The nearly allied Fungvlus 

 einereus is also from high latitudes in the southern hemisphere. 



The sub-family CynthinaB is, with the exception of Cynthia pcupietensis, confined to 

 the southern hemisphere, but none extend beyond the parallel of 40°. Microcosmus bas 

 one species near the equator, while the remaining two are from much further south. In 

 the genus Cynthia, also, most of the species are from the Southern temperate zone, three 

 only being found in tropical latitudes. 



The sub-family Styelinse is represented by three species north of the equator, while the 

 remaining twenty-two are from the southern hemisphere, and the great majority of them 

 from south of 30° S. latitude. 



In the genus- Styela, all the species, with the exception of one (Styela clava) from 

 the northern hemisphere, are from the southern temperate region, and most of them are 

 from between the parallels of 30° and 40° S. 



