REPORT ON THE PTEROPODA. 
97 
De Blainville criticises the figure of Peron and Lesueur , 1 and affirms that the animal 
is turned in the wrong direction in relation to the shell. He figures Cymbulia with the 
animal turned in the opposite direction . 2 But his characteristic love of criticism is in 
this instance at fault, for it is in his figure that the animal is inverted. The uncertainty 
as to the orientation of the animal in relation to the shell is doubtless due to the readiness 
with which shell and animal are separated, and the difficulty of preserving the specimens 
in their natural position. The same reason has led some authors to assert in regard 
to Cymbulia what has been affirmed of the female Argonauta, that the shell was not 
produced by the animal at all . 3 
In regard to the position of anterior and posterior extremities of the shell and of the 
animal, Woodward’s Manual of the Mollusca, which has been followed by all subsequent 
treatises, represents the pointed extremity of the shell of Cymbulia peroni as anterior, 
and the truncated end as posterior. Macdonald , 4 however, does not accept this state- 
ment, but gives a diametrically opposite interpretation. According to him the truncated 
extremity is anterior. Both these conclusions are inaccurate. 
The source of error lies in the external differences between the shell of Cymbuliidse 
and those of C'avoliniidse, and in the great elongation of the dorso-ventral axis, which 
has led to its being regarded as antero-posterior. 
To elucidate the true orientation of the shell, it is necessary to make an examination 
of the animal itself. An investigation of the latter shows that the pallial cavity, which 
in all the Thecosomata (except the Lima- 
cinidse) opens ventrally, in consequence of 
a secondary process to be explained in the 
Anatomical Report, opens in Cy mbulia peroni 
in the direction of the truncated extremity 
of the shell. This extremity ought therefore 
to be considered as ventral. On the other 
hand, the dorsal portion of the animal, as 
determined by the position of the tentacles, 
is situated on the side of the pointed end. 
This extremity is therefore to be regarded 
as dorsal, and the antero-posterior axis of the shell is the short axis at right angles to 
the surface of the fins. 
Among the forms referred to this genus only one is well known. There is also a 
second new form of which unfortunately only the shell is known. 
Fio. 1 
Sagittal section of a Cymbulia ; a, shell ; b, fin ; c, ventral 
lobe of the foot and its whip-like process ; d, visceral mass ; 
e, pallial cavity ; /, alimentary canal. 
1 Histoire de la famille des Mollusques Ptdropodes, Ann. Mus. Hist. Nat . Paris, t. xv. pi. iii. fig. 10. 
2 Manuel de Malacologie, pi. xliii. fig. 3. 
3 Cantraine, Malacologie mediterrandenne et littorale, Mdm. Acad. Sci. Bruxelles, t. xiii. p. 35. 
4 On the General Characters of the Genus Cymbulia, Proc. Roy. Soc., vol. xxxviii. p. 251. 
(ZOOL. CHALL. EXP. — PART LXV. — 1887.) 
Ttfc 13 
