204 EXPEDITION OF THE '• ALr.ATKOSS," 1899-1900. 



where it is at least three times as wiJe as elsewhere, fig. 7. Its nuclei are 

 arranged in bunches running across the muscle and giving it a banded appear- 

 ance, figs. 7 and 8. Under the atrial tentacle the nuclei are more irregularly 

 scattered than elsewhere. The mid-atrial muscle is absent (?). At least 

 a prolonged search has failed to reveal it. Its absence is probably correlated 

 with the extreme shortness of the atrial chamber. 



The oesophagus is cone-shaped, resembling that of P. atlantlcum, but 

 instead of entering at the end, it runs back in a fold of the stomach and 

 enters it near the centre, fig. 4. The compactness of the whole digestive 

 tract is characteristic. Instead of spreading across nearly the entire end of 

 the branchial sac, it is confined to a space not much larger than tiie stomach. 

 In fact, from the right side, only the stomach is visible, PL I, fig. 3. The 

 digestive tract is situated a little to the dorsal side of the median line. Both 

 the endostyle and row of dorsal languets approach it, and as a result curve 

 around under the rows of stigmata. Tlie endostyle is very strongly bent, 

 fig, 3. 



The peripharyngeal band is not closed on the dorsal side, but turns back- 

 ward, forms a large angle about the dorsal tubercle, and extends along the 

 dorsal side of the zooid — another point of reseml)lance to P. spinosum. 



The large ganglion, PI. II, fig. 6, has two large and two smaller nerves 

 arising from its posterior end. At the anterior end there are two large ones 

 and two pairs of smaller ones. The duct of the gland is long and bent near 

 its middle. 



The shape of the atrial chaml)er somewhat resembles that figured by 

 Seeliger for young zooids of P. u/laniiciim var. laevatum. It is shallow and 

 very broad, and the opening is large, figs. 2 and 3. The presence of the 

 tentacle on its dorsal edge is distinctive, however. As is sliowu in PI. II, 

 fig; 7, this is formed of mantle alone. The test about the atrial orifice 

 stops at its base. For a short distance on each side of it the mantle is nuich 

 thickened. The edges of the tentacle are also thickened. 



There does not seem to be as nuich difference as usual between the 

 ventral tentacle and the other smaller branchial tentacles, PI. I, fig. 3. 

 This seems due both to the ventral tentacle being somewhat smaller and the 

 others somewhat larsrer than usual. 



