26 SACCATE. 



Suborder SACCATE Agassiz. 



Saccatce Agass. Cont. Nat. Hist. U. S., HI. p. 293. 1860. 

 CallianiridcE Esch. Syst. der Aeal., p. 21. 1829. 



Family MERTENSIDtE Agass. 



Mertensidcc Agass. Cont. Nat. Hist. U. S., HI. pp. 196, 293. 1860. 



MERTENSIA Less. 



Mertensia Less, (jion Gegenb.). Zooph. Acal., p. 100. 1843. 



Mertensia ovum Morch. 



Cijdippe {Mertensia) ovum Morch. In Nat. Bid. til en Besk. af Gronland, p. 97. 1857. 



Beroe ovum Fab. Faun. Groenl. 1 780. No. 355. 



Beroe cucuUus Mod. Svensk. Vet. Ak. Nya Handl., XI. 1790. 



£eroe ;)i7eus ScoR. (nee Fab. nee Miill.). Arct. Reg., II. PI. XVI. Fig. 4. 1820. 



Cydippe ovum EscH. Syst. d. Acal., p. 25. 1829. 



Cijdippe cucuUus EscH. Syst. d. Acal., p. 25. 1829. 



Mertensia Scoresbyi Less. Zooph. Acal., p. 100. 1843. 



Cydippe cucumis Less. (syn. not correct). Zooph. Acal., p. 105. 1843. 



Mertensia cucullus Agass. Cont. Nat. Hist. U. S., III. p. 293. 1860. 



The comjDression of Mertensia coincides with that of Pleurobrachia. 

 The axis passing through the tentacular apparatus is more than twice 

 as long as the coeliac diameter. What is very characteristic of this 

 genus is the great distance at which the lateral chymiferous tubes aie 

 placed from the digestive cavity, and the close connection which is 

 shown there to exist between the tentacular apparatus and the lateral 

 tubes, the base of the tentacular apparatus seeming to give rise to 

 this long, slender tube, enclosing the digestive cavity in its two wide 

 arches, when seen from the broad side. (Fig. 29.) The spherosome 

 rises so much above the opening for the passage of the tentacular appa- 

 ratus, that it seems, in adult specimens, as if the tentacular ambulacra 

 were the longest. 



Only one large adult specimen of this jelly-fish has been taken in 

 our Bay. It was at first mistaken for a large Pleurobrachia ; but the 

 great flattening of the spherosome, and the peculiar spiral motion 

 which they keep up while active, soon enables one to distinguish them 

 readily from that genus, while swimming in the water. The color, also, 

 is of a light-pink hue ; the spermaries are of a very lirilliant crimson, 

 the ovaries being more dull. It has the rosette of an Idyia, with the 



