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J.A. ALLEN AND H.L. SANDERS 



vessels 'Sarsia' and 'Discovery'. In addition to these, deep-sea 

 bivalves from a series of French expeditions using the research 

 vessels 'La Perle', 'Cryos' and 'Jean Charcot' were kindly donated 

 by our French colleagues. At present this material, other than the 

 types of new species and cited specimens, is housed at the Woods 

 Hole Oceanographic Institution and the University Marine Biologi- 

 cal Station Millport. On completion of our studies, it is our intention 

 to return the French collections to the Museum National d'Histoire 

 Naturelle, Paris and our own collections to the U.S. National Mu- 

 seum and the Natural History Museum, London. 



Museums are abbreviated as follows:- ANSP - Academy of 

 Natural Sciences, Philadelphia; BMNH - Natural History Mu- 

 seum, London; MCZ - Museum of Comparative Zoology, Harvard; 

 MNHN - Museum National d'Histoire Naturelle, Paris; SAM - 

 South Africa Museum; USNM - United States National Museum, 

 Washington, D.C.; ZMHU - Zoologisches Museum, Humbolt- 

 Universitat, Berlin; ZMUC - Zoological Museum, University of 

 Copenhagen. 



Sampling gear is abbreviated as follows:- AD - anchor dredge; CP 

 - beam trawl; CV - Blake trawl; DS - epibenthic sledge Sanders 

 (COB); ES - epibenthic sledge (WHOI); KG - USNEL boxcorer; 

 OS - epibenthic sledge (SMBA); WS - epibenthic sledge (IOS). 



ABBREVIATIONS TO THE TEXT-FIGURES 



SR siphonal ridge 



SS style sac 



ST sensory tentacle 



SM stomach 



VG visceral ganglion 



Family Neilonellidae Schileyko 1989 



Shell usually robust, inflated, moderately large, not particularly 

 elongate, more or less ovate, shell posteriorly extended to some 

 degree and may be acutely rounded or carinate, usually marked 

 concentric sculpture; umbo prominant, anterior to midline; hinge 

 teeth taxodont, continuous or interrupted below the umbo; ligament 

 external, sometimes with an internal component; siphons present; 

 hind gut either a single loop or a series of loops and coils to the left 

 and right of the body. 



The family comprises four genera, Neilonella, Pseudotindaria, 

 Neilo and Pwtonucida (Allen and Hannah, 1986). By reason of their 

 external ligament, the neilonellids in the past have been included in 

 the family Malletiidae, however this family was shown to be an 

 assemblage of unrelated taxa and is now much restricted (Sanders 

 and Allen, 1985). The robust, ovate, concentically ridged shells of 

 the neilonellids are in marked contrast to the thin, translucent, 

 elongate shells, lacking any marked concentric sculpture, of the 

 malletiids. 



AA 



anterior adductor muscle 



AN 



anus 



AR 



anterior pedal retractor muscle 



AS 



anterior sense organ 



BG 



'byssal' gland 



CG 



cerebral ganglion 



CM 



caecum 



CV 



cerebro-visceral commissure 



DD 



digestive diverticula 



DH 



dorsal hood 



DT 



digestive ducts 



FA 



feeding aperture 



FG 



fused gill tissue 



FR 



faecal rod 



FT 



foot 



GA 



gill axis 



GI 



gill 



GP 



gill plate 



GS 



gastric sheild 



HG 



hind gut 



HP 



hinge plate 



HT 



hinge teeth 



LI 



internal ligament or resilium 



LO 



opisthodetic external ligament 



MG 



combined mid gut 



MM 



mantle margin 



OE 



oesophagus 



PA 



posterior adductor muscle 



PE 



sensory papilla 



PG 



pedal ganglion 



PL 



palp 



PP 



palp proboscis 



PR 



posterior pedal retractor muscle 



PS 



posterior sorting area 



SE 



siphonal embayment 



SP 



combined siphon 



Genus NEILONELLA Dall 1881 



TYPE SPECIES. Leda (Neilonella) corpulenta Dall 1881; OD. 



Shell moderately robust, relatively wide, strong concentric sculp- 

 ture, anterior margin rounded, posterior margin slightly attenuate 

 and may be acutely rounded, not carinate; umbo prominant, anterior 

 to the midline; hinge plate moderately strong, many chevron teeth, 

 small gap between anterior and posterior series; external ligament 

 opisthodetic, inserting in an external gutter in each valve, with 

 minute internal resilifer, siphonal embayment shallow; hind gut 

 single loop to the right of the body. 



Genus PSEUDOTINDARIA Sanders and Allen 1977 



TYPE SPECIES. Pseudotindaria erebus (Clarke 1959); OD. 



Shell robust, relatively wide, anteriorly and posteriorly rounded, 

 not carinate, strong concentric sculpture; hinge plate strong with 

 numerous chevron teeth continuous below umbo; ligament external, 

 anterior part short, posterior part elongate; hind gut with complex 

 series of loops and coils to the right and left of the body. 



Genus NEILO Adams 1854 



Type species. Neilo cumingii Adams 1854; by monotypy. 



Shell robust, relatively wide, moderately elongate and posteriorly 

 extended, postero-dorsal margin straight or slightly concave, cari- 

 nate, posteriorly truncate or slightly rostrate, postero- ventral margin 

 may be somewhat sinuous, two rounded radial ridges from umbo to 

 posterior margin, concentric sculpture; hinge plate well-developed; 

 numerous chevron teeth, anterior and posterior series separate and 

 may differ in size (anterior larger); ligament external. 



