o. t o "TERRA NOVA" EXPEDITION. 



./.) consists of ;i swollen base continuous with the palp, and, like it, lined by a deep 

 glandular epithelium, and of a thin membranous extension (Fig. 11, ''''/.) by which its 

 free edtre is made to overhang the mouth and lower lip like a curtain. This extension 

 is covered by a thin non-glandular epithelium, and terminates abruptly at the junction 

 of the lip with the palp. 



Heart- The ventricle of the heart is perforated by the intestine ; the auricles 

 are voluminous and communicate with one another beneath and behind the ventricle 

 (Fig. 10, an./:), and show in their posterior region a feeble development of pericardial 

 gland-tissue. 



Renal On/anx. The kidney is more complicated by labyrinthine folding of its 

 walls than in the Arcidae. It opens close to its anterior end by a short duct into a 

 small sinus common to it and to the genital duct. On a plane slightly posterior to 

 this lies the reno-pericardial duct, which passes from the anterior region of the 

 pericardium across the literal surface of the kidney to its ventral wall. The two 

 kidneys are quite separate from each other, but towards their hinder end are closely 

 applied and fold in between the posterior pedal retractors, differing apparently in this 

 particular from the kidneys of Pectuncuhis (8, p. 300). 



Gills. The gill-axis, as noted by Pelseucer, is extremely large and muscular. 

 The muscles, as in other Arcacea, consist of two bands situated at the base of each 

 demibranch, and take their origin from the shell just above the anterior extremity of 

 the gills (Fig. 10, fn-.-m.). Although these muscles are remarkably well developed they 

 constitute a small part only of the gill-axis (Fig. 12, ?.), which is composed mainly of 

 a cartilagiuoid connective tissue (Fig. 12, <:}. 



The filaments of both demibranchs are reflected, and are united by ciliated discs 

 at about the mid-region of both descending and ascending arms. So far as could be 

 observed, there is also ciliary connection between the filaments at the angle of reflexion 

 and at their free extremities. There are no iuterlaminar unions. 



PHILOBRYID^E. 



5. Phililri/a lunoidcs, Smith. PI. Ill, figs. 13-15. 



Stations 331 and 340. A few specimens dredged in 250 and 160 fathoms off the 

 entrance to McMurdo Sound. 



The anatomy of an allied species, Philobri/a suhlcvvis, has been described by 

 Pelseneer in his Report on the Collections of the S.S. "Belgica" (12, p. 42), and in 

 most particulars of any importance his description of that species applies equally well 

 to P. liiitoiilt'x. The following few additional notes seem, however, of sufficient interest 

 to lie recorded : 



Mantle and Foot. The mantle-border has no eye-spots or tentacles ; its edge in 

 cross-section closely resembles that of Lixxurca (PL I, fig. 2), except that the outer 

 fold is smaller, the middle slightly more pronounced, and the inner more swollen. The 

 byssus is strong, with a solid root broken up into about thirty filaments. 



