636 R. C. PUNNETT. 
INTERNAL STRUCTURE. 
Proboscis. The outer circular muscle layer is very delicate. The proboscis contains a 
central cavity which is not divided into right and left portions in front of the central 
complex. The long vermiform process of the stomochord runs forwards dorsal to the cavity 
(Pl. XLI. fig. 8, v.). It is somewhat fragmented in places. Where it joins the stomochord 
proper appears the ventral septum separating the ventral coelom into two portions, which 
do not subsequently jo with one another. A dorsal septum also occurs in front of the 
junction of the pericardium with the basement membrane below the epidermis. The lumen 
of the stomochord is well marked in some places though obliterated in others. The lumen 
of the lateral diverticula is only patent at the extremity of each. The chondroid tissue is 
well developed. The nuchal skeleton possesses a well-marked keel. 
The left proboscis pore alone is present. The right perihaemal cavity reaches forwards 
considerably further than that of the left side (Pl. XLI. fig. 6, ph.). 
The pericardial auricles are very short. 
Collar. The outer longitudinal muscles are poorly developed and there is no circular 
layer. The collar is without a cavity. The dorsal septum extends through the length of 
the collar, whilst the ventral one is only found complete at the posterior end. 
The nerve cord is practically solid throughout, only very faint traces of a lumen being 
discoverable here and there. There is no sign of any dorsal root. 
The cornua of the nuchal skeleton are long and reach backwards to the extreme hind 
end of the collar (Pl. XLI. fig. 8, cn.) and to some extent overlap the branchial region. 
The collar pores open into the first gill pouch, which possesses a small diverticulum 
reaching forwards for a short distance ventral to the collar canal (Pl. XL. fig. 8, p.1). This 
is doubtless the structure referred to by Willey (99, p. 280) as the truncal canal. In 
the present species it possesses no trace of an opening into the perihaemal space, and the 
diverticulum differs in nowise histologically from the rest of the gill pouch, thus lending 
no support to the morphological importance with which Willey is inclined to regard them. 
Trunk. The circular musculature is, as usual in this genus, found inside the longitudinal 
layer. In the branchial region the ventral portion of the cesophagus is almost as large as 
the branchial division, the proportions being similar to those in Sp. porosa as figured by 
Willey ’99, Pl. XXXI. fig. 45). About nine synapticula are present on each gill bar. A 
distinct but small post-branchial groove is present (Pl. XLII. fig. 20). The grooves into 
which the gill pouches open are produced backwards past the branchial region. They do 
not however exhibit the peculiar depressions found in Sp. porosa and Sp. alba which Willey 
has termed dermal pits. Too much stress must not be laid on their absence, however, as 
the gonads are somewhat immature and it is possible that with their increase in size small 
dermal pits might arise. There is little doubt that they would never reach the same 
development as in the above-named forms, a circumstance probably correlated with the smaller 
size of the species under consideration. 
In the branchial region both median and lateral gonads are present. In the genital 
region however the lateral gonads alone are present. The median gonads are always very 
small and are not nearly so numerous as the lateral ones. 
Though the above species has been created on the strength of a single imperfect 
specimen yet in its short collar, its undivided proboscis cavity, the reduction or absence of 
