250 "TERRA NOVA" EXPEDITION. 



situated below and close behind the anterior adductor. The siphons are large and 

 highly muscular, but capable of only partial retraction ; externally they are covered by 

 a thick rugose periostracum. No ocular tentacles were observed. 



Foot. Although the foot was considerably shrunken, it is obviously of consider- 

 able size iii the natural condition. Upon its ventral surface is a narrow byssal groove, 

 though no byssus was attached to it. 



The pedal muscles are unequally developed. The anterior retractors, which arise 

 in the usual position close behind the anterior adductor, are of quite average develop- 

 ment ; the posterior retractors, on the other hand, are very much reduced, and show 

 signs of degeneration not only in the quantity but in the structure of their components. 

 Their origin was destroyed, but they evidently arise as usual in front of the posterior 

 adductor, and pass thence enfolded in the posterior part of the renal organ into the 

 hinder end of the visceral mass. When exposed by the removal of the kidney they 

 present a hard, sharply defined appearance more like that of a rod of cartilage than a 

 muscle of the ordinary type. Examined microscopically, they were found to consist 

 mainly of a peculiarly dense form of fibrous tissue, interspersed with a relatively small 

 proportion of muscle-fibre a structure more nearly that of a ligament than of an 

 ordinary active muscle. 



Digestive Organs. The lips and palps are voluminous, the latter being triangular 

 and freely pendent, with their apposed surfaces strongly fluted. The general dis- 

 position of the stomach and intestine is similar to that described and figured by 

 Lacaze-Duthiers (4, p. G93) for Aspergillum. The commencement of the intestine 

 (gastrp -intestine) is partially divided into right and left channels by a pair of longi- 

 tudinal folds. Neither of these cavities contained a crystalline style, but within the 

 stomach was a cuticular secretion (fleche tricuspide) of remarkable development. This 

 secretion is stated by Pelseneer (10, p. 215) to be also highly developed in Lyonsiella. 



The intestine is of large calibre, but, owing to the fact that it is flattened and 

 considerably coiled, it appears when superficially exposed (as represented in Fig. 20) 

 to be of variable diameter in different parts, according as its narrow edge or flattened 

 surface is presented to view. In its final upward bend it, in fact, narrows considerably. 

 It enters the pericardium and traverses the heart in an almost vertical direction before 

 bending backwards towards the upper surface of the adductor. 



Renal /mil Generative Organs. The bulk of the kidney (Fig. 20, ?) is wedged between 

 the pericardium and the adductor, as is common in the Auatiuacea. It is compressed 

 autero-posteriorly with its chief axis almost vertical, much as described by Odhuer 

 (8, p. 341), fig. 35A) for Pandora. This orientation is unusual ; as a rule in this group 

 the kidney is much elongated with its long axis horizontal. It is so in the genera 

 described by Odhner, with the above exception, and also to a marked degree in a 

 specimen of Anatina truncata which I have had an opportunity of examining. Before, 

 however, concluding that A. elliptica is peculiar in this respect, it must be borne in 

 mind that the damage to the adductor in this particular specimen (the muscle appears 



