ANATOMY <>F PELECYPODA l:T 1! Mi. -.'17 



The reno-pericardia] duct ( Fi^. K;. r.pc.d.} arises from tin- lateral border of the 

 pericardium sunn- little way behind it* forward extremity. ,-md passes across the outer 

 *t</<- of tin.' saecular distal arm of the kidney to reach its ventral surface. Slmrtlv before 

 its communication with the main cavity of the kidnev it receives the ncniial duet 

 (Fiu\ Hi. </.'/.). The two capacious distal arms of the kidiiev are widelv united 

 beneath- the pericardium, close in iVoiit of the addm-ior (Fjo-. M;. r.c.). 1'osterior 



to this Communication eacli is prolonged upon the surface of the addllctoi- nearK 



as far as tlie visceral ganglion and dose to its termination opens to the exterior 

 (Fi.u. K;. ,-..). 



The sexes are separate. 



<////*.- The gills a iv similar in structure to those of other memliers of the genus. 



The chief filaments resemble in cross-section most nearly those of /.////,/ in/l,it,i 

 (Eidewood. 17. p. -15); there are twelve filaments to the pleat. The apical filament^ 

 are unmodified. Interlaminar unions occur between the chief filaments and extend for 

 some little distance upwards from the angle of reflexion; interfilamentary unions are 

 numerous and roughly alternate in position from pleat to pleat. The individual 

 filaments have no longitudinal intrafilamentary septum. 



The gill-axis contains two stout longitudinal muscle-bands, which, in front, on a 

 level with the upper region of the stomach, become blended with the muscles of the 

 bodv-wall. Similar muscle-bands run along the continuous selvedge that forms tin- 

 free margin of the reflected lamime and along the reflected angle of each demibranch. 

 The hinder end of the gill-axis is not attached simply to the ventral surface of the 

 adductor, as it is in the Arcacea, but extends to the mantle behind the adductor 

 (Fig. 17), leaving, between its inner margin and the edge of the posterior retractor 

 pedis, a small orifice (Fig. 17, <>.) that leads into a space of considerable extent (/.</.), 

 situated upon the posterior and dorsal surface of the adductor, and reaching as far forward 

 as the hinder limit of the pericardium. 



This cavity, which occurs also, though to a less degree, in L. /m///x, is a 

 diverticulum of the mantle-cavity, within the substance of the mantle and gill-axis, and 

 has apparently been developed in relation to the excessive breadth of the adductor, 

 tilling in the lateral parts of the abnormally wide space between the rectum and 

 the insertion of that muscle. 



EULAMELL1BRANCHIATA. 

 ^1 SUBMYTILACEA, CARDITID.K. 



8. ]' l 'iii-i-!'-itnl/i/ /ni/'intrala (Peshayes) ( V> m r'n'iinlin ,nixtrnli, Lamarck .'). I'l. Ill, 

 tig. 18. 



Station l:!4. New Zealand. E. of North Cape. 1 I -JO fathoms. 



So far as can be ascertained from previously published descriptions of the anatomy 

 of genera belonging to this family, there is little of importance to distinguish this genus 



