648 R. C. PUNNETT. 
The racemose organ is always well-marked and in the larger specimens is usually some- 
what lobulated. 
Collar. The cavity in the anterior part of the collar is usually spacious though not 
quite to the same extent as in Pt. parva. The dorsal septum is usually complete after 
the first root. The ventral septum may be entirely absent or, equally as often, it may be 
found in the hinder part of the collar. The number of proboscis roots varies from three 
up to as many as six. The collar nerve cord usually has a distinct and continuous lumen 
which may rarely shew a tendency to become obliterated. The length of the cornua of 
the nuchal skeleton is subject to a good deal of variation. It averages a trifle less than 
a quarter of the collar length. 
Trunk. In the branchial region the number of synapticula varies with the size of the 
animal. The branchial region averages rather more than double the length of the collar 
(p. 665, Table 8). The post-branchial groove is well-developed, its length being about one-fifth 
of that of the branchial region. At its anterior level the genital folds are still of con- 
siderable size (Pl. XLVI. fig. 49), At the end of the post-branchial groove the folds have 
become much reduced (Pl. XLVI. fig. 51). The branchial portion of the cesophagus is 
somewhat smaller in section than the cesophageal portion (Pl. XLVI. fig. 57). A pygochord 
is present in the caudal region. 
Ptychodera flava, var. maldivensis (Pl. XX XIX. fig. 27). 
Locauity, ETc. From Maradu, Addu Atoll, where it was taken from sandy holes of the 
reef-flat. Fairly abundant. Two specimens also obtained from Hulule, on the east reef 
underneath the stones of the boulder zone in sand. 
EXTERNAL FEATURES. In general shape and appearance this variety is indistinguishable 
from laccadivensis to which it is very closely allied. Moreover the coloration in life was 
similar, this variety, like laccadivensis, shewing differentiation of the hepatic caeca into an 
anterior dark group and a posterior larger and lighter group. 
INTERNAL STRUCTURE. Exceedingly similar to that of Jaccadivensis from which variety 
however the present one would seem to differ on the following points. The proboscis cavity 
has a definite outline as in parva (cf. Pl. XLIII. fig. 21) and does not reach up among 
the radial muscle bundles as in laccadivensis (cf. Pl. XXXIX. fig. 25). 
The racemose organ is on the whole somewhat smaller. 
The dorsal roots are Jess numerous, a feature in which this variety resembles cooperv. 
The cornua of the nuchal skeleton are relatively shorter than in laccadivensis. 
The branchial portion of the cesophagus is as large or larger than the ventral portion, 
whilst in laccadivensis it is always smaller. 
The branchial region is relatively shorter than in laccadivensis, averaging only 1°63 times 
the collar length as against 2°26 times in the latter variety, a difference which is the more 
striking when one takes into account the comparatively large number of specimens examined 
(see below, p. 665, Table 8). 
The post-branchial groove of maldivensis is also somewhat shorter than that of laccadivensis. 
In point of size the present variety is considerably smaller than Jaccadivensis, preserved 
specimens of which may be as much as 150 mm. in length, whilst the largest specimen of 
