PLATE IV. 



Fig. 1. Cuspidana fvagilissima, Smith. 



Fig. 1. The animal seen from tlie right side, the mantle having been removed up to its union with the 



hranchial partition. 



b, Anterior palp ; d, foot ; c, branchial partition ; /, visceral mass ; ;;, orifice in the partition ; i, free margin 



of tlie mantle (pcilal orifice) ; j, point where the two lobes of the mantle are united posteriorly to the 



pedal aperture ; I, anterior adductor ; m, posterior adductor ; p, siphons ; r, lateral muscles of the 



lirancliial partitions. 



Fig. 2. Cuspidana curta, Jeffrey.s. 



Fig. 2. The muscular partition seen ventrally. 



a, Buccal aperture ; other letters as in fig. 1. 



Fig.s. 3, 4. Cuspidana 7'ostrata, Spengler. 



Fig. 3. Tlie animal seen from the ventral aspect, the mantle having been removed from both sides. 



/(, Jlembrane uniting the muscular partition to the mantle ; k, internal aperture of the branchial siphon ; the 

 other letters as in the figures above. 



Fig. i. The animal seen from the right side, the mantle having been removed up to its union with the 

 branchial partition. 

 e, Posterior palp ; n, posterior retractor of the foot ; the other letters as in the figures above. 



Fig. 5. Cuspidana platensis, Smith. 



Fig. 5. Labial palps seen ventrally. 



Letters as in the jireceding figures. 



Fig. 6. Cuspidana. 



Fig. G. Diagrammatic sagittal section, passing through the median plane. 



h. Cerebral ganglion ; n, anterior retractor of the foot ; n', posterior retractor of the foot ; 0, heart ; p, sagittal 

 partition of the dorsal chamber ; 7, anus ; r, kidney ; .s, branchial siphon ; t, anal siphon ; u, partition 

 separating the two siphons ; f, free end of the anal siphon ; w, common sheath of the two siphons ; the 

 other letters as above. 



Fig. 7. Lyonsiella jeffreysi, Smith. 



Fig. 7. Diagrammatic transverse section. 



a, Mantle ; h, pedal aperture ; c, foot ; d, visceral mass ; f, gill ; h, dorsal or anal chamber ; i, ventral 

 chamber. 



Fig. 8. Lyonsiella abyssicola (Sars). 



Fig. 8. Diagrammatic transverse section. 



/, Membrane uniting the gill to the mantle, and forming along with it the branchial partition ; other letters 

 as in fig. 7. 



Fig. 9. Cuspidana. 



Fig. 9. Diagrammatic transverse section. 



e, Muscular portion of the branchial partition ; .7, orifice which pierces it ; other letters as in figs. 7, 8. 



Fig. 10. Gills of Pelecypoda. 



Fig. 10. Diagrammatic transverse sections of the right giU of different types of Pelecypoda : — 



A, Malletia; B, Nucula ; BB, Solenomya ; C, A hypothetical type, really unknown; D, 

 Area; E, Unto; F, Canlium ; G, Telh'na ; II, Lucina ; I, Lyonsia. 



a, Direct lamina of the outer plate ; a', reflected lamina of the outer plate ; a", appendage ; 6, direct lamina 

 of the inner plate ; b', reflected lamina of the inner plate ; c, point of attachnjent of the gill. 



