ANATOMY OF PELECYl'oDA r.lKXE. -_M. r , 



Digestive <>r</iin.x. The alimcntarv canal, and tlic relation of tin- rectum to tin: 

 heart, are the same as in Pectcn. 



lu'iinl and Gi'iK'nifiri' <h-i/nii*. The renal organs are of (he /'/,// type, with the 

 external orifice situated at the posterior end, and the reno-pcricardial duct in front. 

 L T pon the auricles is a very considerable accumulation of pericardia! gland-tissue. 



The sexes are separate (the specimen examined was a male), hut the opening of 

 the gouad to the exterior could not be traced. 



(I///*. The gills are of the 1'i'rfr/i type, filamentous and deeply pleated, \\ith ten 

 ordinary filaments to the pleat, and enlarged chief tilaments ai the re-entrant angles. 

 The filaments at the projecting angles are not modified. 



The filaments of both demihrandis are reflected, and are united at numerous 

 levels by cilia borne upon prominences that project towards the inter-laminar space. 

 The cavity of each filament is divided by a longitudinal septum, attached on cither side 

 to a prominent thickening of its chitiuous lining. 



OSTR/EACEA. 

 LIMIDJv 



7. I /unit (Limn/ida) /tixlyxoiti. Smith. H. III. figs. 1(5, 17. 



Station >!!. Two bottles, containing numerous specimens dredged olf ('ape Bird, 

 McMurdo Sound, in 250 fathoms. 



Compared with other species of Lima (for instance, L. hians, L. I'lliptint) the 

 animal is relatively long from the hinge to the adductor. The organs situated in this 

 region (heart, kidney, etc.) are therefore not so much cramped as in these and other 

 species of Limn, and show on the whole a less specialised and apparently more primitive 

 condition. 



Mantle.- The mantle has the structure commonly found in the genus (7, p. '20), 

 with a voluminous curtain, beset on its inner surface with many tentacles. The 

 tentacles, although well developed, are scarcely so numerous as in certain other species 

 (e.t/., L. liinn*}. Nowhere do they exceed from three to four rows, and anteriorlv. in 

 the reo'ion in which the curtains are united, are reduced to a single row. 



o o 



Mum-lex and Font. Upon the upper edge of the adductor is a small muscle 

 (Figs. Hi, 17, m.) which, at first sight might easily, from its area of origin, he mistaken 

 either for the retractor pedis. or fora specialised portion of the adductor. It is, 

 however, in reality part of the mantle-musculature, and passes towards the middle line 

 into tin- base of the curtain a short distance in front of its dorsal closure. 



The pedal retractors are remarkably weak : the posterior seem to lie absent, hut in 

 place of them (functionally) are two small muscles (Figs. H'>. I 7. /<././<.) that arise from 

 the mantle-border Ix-liiinl the adductor, as described by Pelseneer (l6-\. p. :i4), and pass 

 across its posterior surface to the hinder part of the visceral mass and foot. The 

 anterior retractors have no clearly defined origin from the shell, but are formed bv the 



