EEPOET ON THE NTJDIBBAN CHIATA. 
7 
Acura, H. and A. Adams. 
Acura, H. and A. Adams, Genera of recent mollusea, vol. ii., 1858 (part ix., 1855), p. 98. 
„ Eergh, Malaeolog. Untersuch., loc. cit., Heft v. pp. 241-246. 
Cauda corporis elongata filiformis. 
This genus was established by H. and A. Adams, but remained almost entirely 
unknown until the publication of my Monograph. I then showed that the two genera 
Acura and Phylliroe could not be distinguished by any essential external characters, 
and exhibited no great differences in their internal structure. I was however unable, 
owing to the bad state of preservation of the specimens, to find a renal organ in Acura. 
My renewed examination of the animal has clearly shown the presence of this latter 
organ. The only character by which Acura can be differentiated from Phylliroe is 
by the presence inthe former of a pointed, elongated, mostly filiform tail ; and even 
this in one species ( Acura lanceolata, Bgh.) is rather short, and thus establishes a link 
between Acura and Pliylliroe. 
In its biological relations the genus Acura very probably entirely agrees with 
Pliylliroe. 
Only two species are known : — 
1. Acura lanceolata, Bgh. 
Philippine Sea, Pacific. 
2. Acura pelagica, Ad. 
Atlantic. 
1. Acura pelagica, H. and A. Adams (PI. X. fig. 4). 
Acura 'pelagica , H and A. Adams, loc. cit., p. 98, pi. lxx. fig. 4. 
„ „ Bergh, Malaeolog. Untersuch. (in Semper, Eeisen im Archip. d. Pliilipp., Th. II. 
Bd. ii.) Heft v. pp. 242-246, Taf. xxx. figs. 6-19 ; Taf. xxxi. figs. 3, 4. 
Five specimens of Acura pelagica were captured in the East Atlantic, off the 
coast of Africa, on August 16, 1873, and in the South Atlantic, on October 14, 1873. Some 
specimens were preserved in alcohol, others mounted on slides. 
The length of the body (excluding the rhinophoria and the tail) is from 7 to 8 mm. ; 
the tail is nearly as long as or even a trifle longer than the body ; the rhinophoria were of 
the usual length. The colour was quite typical. The form of the body is rather more 
elongated than in Pliylliroe, but not so high ; in one individual the penis was everted, 
and appeared to be almost equal in length to the body. 
The central nervous system entirely resembles that of Phylliroe, as do also the eyes 
and the otocysts ; the latter organs are visible beneath the eyes as chalk-white points, 
they each contain from 150 to 200 otoconia. 
