THE ENTEROPNEUSTA. 655 
The cornua of the nuchal skeleton are short, extending over less than } of the collar 
length. 
Trunk. The branchial region is fairly long, averaging more than double the length of 
the collar in 10 specimens (see Table 12, p. 673). In one small specimen only was it 
less than double the length of the collar. On the whole it is remarkably constant in length. 
The branchial division of the cesophagus is considerably less than the ventral portion. The 
post-branchial canal was found to be short in the specimen examined, being less than } of 
the length of the branchial region. The post-branchial pre-hepatic genital tract is compara- 
tively short. The genital pleurae are well-developed. 
Ptychodera flava, var. cooperi (Pl. XX XVIII. fig. 12; Pl. XLV. figs. 45—4/7). 
Locatity, ETc. Two specimens, both somewhat imperfect, from N. Male Atoll. Dredged 
in 5 fathoms on a sandy bottom within the velu of Jaro near Helengeli. 
EXTERNAL FEATURES. A small form with a maximum breadth in the collar and branchial 
region of less than 3mm. Behind the hepatic region the diameter of the animal is only 
a trifle over 1mm. In the preserved specimens the collar and proboscis are both very short, 
their width being greater than their length (Pl. XXXVIII. fig. 12). The genital pleurae 
are large in the branchial region, which is rather more than double the length of the collar. 
The genital region between the termination of the branchial and the commencement of the 
hepatic caeca is relatively long. The hepatic caeca are short but well-developed, and on 
their inner sides are lobulated. There is no distinction into lighter and darker ones. 
INTERNAL STRUCTURE. 
Proboscis. The cavity of the proboscis is well-developed in one specimen, whilst in 
the other it is small. The radial arrangement of the muscles is not so conspicuous as in 
most members of the genus. Dorso-ventral muscles anterior to the pericardium are not 
present, and the ventral proboscis septum is very short. The right proboscis pore in each 
case places the dorsal coelom in communication with the exterior. The left pore is present 
in one specimen but absent in the other. The racemose organ is well-marked but unlobulated. 
The keel of the nuchal skeleton is somewhat larger than usually obtains in the species 
(Pl. XLV. fig. 45). The skeleton is altogether massive (Pl. XLV. fig. 46). 
Collar. The cavity in the anterior part of the collar is very spacious. Posterior to 
it the collar musculature is unusually strongly developed, a fact which may in some measure 
account for the extreme shortening of this region on preservation. The dorsal septum is 
as usual complete after the first root. A ventral septum was completely absent in one 
specimen though traces of it occurred at the extreme hind end of the collar in the other. 
In one case a single dorsal root reaching to the epidermis was found. In the second 
specimen this was supplemented by a rudimentary one. The lumen of the collar cord shews 
a tendency to occlusion behind the level where the roots come off. 
A noteworthy feature of this variety is the condition of the nuchal cornua which extend 
back to the hind end of the collar, the tip of them being found in sections which also 
pass through the first branchial bars. Such a condition is most unusual amongst the 
Ptychoderidae, recalling that recently described by Ritter (OO, p. 113) for Harrimania 
maculosa. 
Trunk. The branchial portion of the cesophagus is rather larger than the ventral portion. 
Seven to eight synapticula are present. The post-branchial groove is large (Pl. XLV. fig. 47), 
84—2 
