644 R. C. PUNNETT. 
Ptychodera flava, var. parva (Pl. XXXVIII. figs. 16, 20, 21; Pl) XXXIX. fig. 26; 
Pl. XLII. figs. 21—28; Pl. XLIV. figs. 30—32; Pl. XLVI. fig. 48). 
Locauity, etc. From Turadu, 8. Mahlos Atoll. About a dozen specimens procured, all 
more or less of the same size. They were dredged from 20 fathoms on a bottom of 
coarse sand. 
EXTERNAL FEATURES. A small, somewhat short and slender form. The proboscis is of 
about the same length as the collar, which measures 2°5—3 mm. long, and is of approximately 
the same width. Behind the branchial region the body is not more than about 2mm. wide. 
The liver saccules are not large and are slightly lobulated in the larger specimens. There 
is no apparent differentiation in colour among them as is usual in this species. The average 
length of the branchial region is about 14 times the length of the collar, it being thus 
comparatively short (wide p. 673). In the single entire specimen the total length was 
only 30 mm, 
INTERNAL STRUCTURE. 
Proboscis. A delicate layer of circular fibrils surrounds the longitudinal muscles which 
are gathered together into radial bundles. A few longitudinal fibres are more closely gathered 
round the central lumen of the proboscis and give it a definite outline (Pl. XLIII. figs. 21, 22). 
Dorso-ventral muscles are always found dorsal to the central complex anterior to the peri- 
eardium. The ventral proboscis septum is well-marked and reaches forwards almost or quite 
to the tip of the stomochord. Both dorsal divisions of the dorsal proboscis coelom are in 
communication with the exterior by the paired and equal proboscis pores (Pl. XLIII. fig. 26). 
In one case the proboscis pores opened together almost in the mid-dorsal line (Pl. XLII. 
fig. 23), a condition of great rarity in this genus and recalling those obtaimmg im Balano- 
glossus apertus (Spengel, 794) and B. jamaicensis (Willey, 799, p. 293). 
The racemose organ is usually well-marked but is never lobulated. The lumen of the 
stomochord anterior to the lateral diverticula may be fairly distinct or almost obliterated. 
The lumen of each lateral diverticulum is large and open at the end but the portion by 
which it would communicate with the central lumen is usually almost or quite obliterated. 
Collar. Beneath the basement-membrane is found a fine but definite layer of longi- 
tudinal muscle fibres. In the anterior part of the collar they are rather better developed 
and here directly enclose a delicate layer of circular muscles. No outer circular layer is 
found over the greater part of the collar. The anterior free cavity of the collar coelom 
is very spacious (Pl. XLIII. fig. 27,c.) extending as usual completely round the cesophagus 
in this region. Inside it are found the inner longitudinal muscles of the collar and within 
these again the peripharyngeal spaces with their enclosed circular muscle fibres. The dorsal 
collar septum is as usual complete immediately behind the first root. In one case it was 
complete just anterior to this structure. The ventral septum may be absent or present in 
the extreme hind portion of the collar. 
The nerve cord exhibits a complete lumen throughout, though sometimes with a faint 
tendency to obliteration. When this occurs the height of the cord as seen in transverse 
section is rather greater than usual and the gland cells are more numerous (cf. Pl. XX XVIII. 
figs. 20 and 21). The number of the dorsal roots is either two or three. The majority 
reach to the ectoderm. 
The cornua of the nuchal skeleton extend over nearly a quarter of the length of the 
collar, Their length is apparently very fairly constant for this variety (cf. Table 1, p. 645). 
