SEMU'ERTEBRATES. 



1 : and that some of them, like the one figured on p. f>(il. arc used as 

 d. To the same subfamily as 7V/c///'*/" also belongs the extensive 

 "eiius Avritl.'n.t, in which tlie outer tunic is soft and flexible, instead of bein^ 

 cartilaginous. A totallv distinct subfamily is, however, indicated by the remark- 

 able deep-sea "vnus // /// >< >1 > )/ /////'.<. of which the two known species were obtained 

 at depths varviii"' from six hundred to two thousand nine hundred fathoms, 

 duriii" the vova-'-e of tlie ( 'Im/friit/t',: Here we tind the cup-shaped or pear-like 



dy at tachetl by n loiio-e]- ( shoi'tei 1 stem: Avhile tlie a])ci'turcs are circular and 



t closed by lobes. The outer tunic is cai'tilaj^'iiious. but soft and thin, although 



icken.-.! in places to form plates. Tin; internal longitudinal bai's usually found 



the branchial chamber a re *vant in^ in this ^-cnus : th(; ^'ill-slits are small and 



H'ularly placetl ; and the \-iscera form a com])act iri'ee'ular mass on the dorsal 



'' "1 this chamber. In the species here figured ( //. ('(ili/coddH), which is tVom 



N'oi-tli Pacific, the stem is of ^reat leiio'th. ami the outei 1 tunic thickened so 



1() loi-m a number of nodules or plates: but in the South Atlantic form (//. 



