108 



J.A. ALLEN AND H.L. SANDERS 



Fig. 10. Neilonella hampsoni. a, lateral view of the hinge plate of the 

 right valve of a paratype; b, dorsal view of the shell of the holotype. 

 Both specimens taken from Atlantis II station 155 from the Sierra Leone 

 Basin. Scales = 1mm. 



with horizontal midline, posterior limit of shell immediately ventral 

 to mid line; hinge plate stout extending along most of the dorsal shell 

 margin, anterior and posterior tooth series meet below umbo, with 

 faint suggestion of an edentulous space between, 1 3 posterior and 1 

 anterior teeth in specimen 3.9mm total length, teeth increase in size 

 distally, teeth chevron-shaped, obtuse, so much so that teeth appear 

 to be a straight line transverse to hinge plate; ligament opisthodetic, 

 external, short, anterior outer layer extremely short, hidden beneath 

 umbo, no resilium. 



Maximum total length of present specimens is 7.5mm. 



Apart from N. salicensis, from which it differs in having a shorter, 

 wider shape, and well-marked lunule and escutcheon, the only other 

 protobranch species with which it has some similarity is 'Leda' 

 sericea var ovata Jeffreys 1 876 (Jeffreys, 1 879). One of us ( JAA) has 

 examined specimens of this latter species in the Natural History 

 Museum, London, (BMNH 85 1 1 5483-84) and find that L. sericea 

 is more ovate, with the dorsal margins much less sloping, a more 

 anteriorly positioned umbo and a much more narrow hinge plate. 



Internal morphology 



The morphology is similar to Neilonella salicensis. Such differences 

 that do exist include the adductor muscles, both of which are small, 

 similar in size, but with the posterior oval and the anterior round in 

 cross section. The foot is somewhat smaller but with a moderately 

 large byssal gland with a small, hooked, median papilla posterior to 

 its aperture. Except for the posterior quarter of their length, the 

 margins of the divided foot are finely papillate. There are approxi- 

 mately 20 gill plates and 25 ridges on the palps of a specimen 3.9mm 

 total length. The hind gut makes a simple loop to the right side of the 

 body, it has a wide lumen (0.21mm in diameter) with a single well- 

 defined typhlosole running its entire length. The stomach is large 

 and the mouth lies some distance posterior to the inner wall of the 

 anterior adductor. The kidney extends in a narrow band from the 

 posterior margin of the posterior adductor, anteriorly narrowing over 

 the viscera, and terminating at the posterior edge of the digestive 

 diverticula. 



It is named after our good friend and colleague George Hampson 

 who accompanied us on so many of our cruises and without whom 

 sampling at abyssal depths would not have been the resounding 

 success that it proved to be. 



Neilonella corpulenta (Dall 1881) 



Type locality. Blake station off Havana, 823m (station number 

 not recorded but, only station 51, 23°1 1.0'N 82°21.0'W, is listed as 

 having a depth of 450fm (823m) (Smith, 1888)). 



Type SPECIMEN. Holotype, U.S. National Museum 63169. Cited 

 specimen: BMNH 1995048. 



Leda (Neilonella) corpulenta Dall, 1 88 1 , 1 25; 1 886, 254, pi. 7, figs. 



la, lb. 

 Neilonella (N.) corpulenta Laghi 1986, pl.9, figs 1-3. 



Material: 











Cruise Sta 



Depth No 

 (m) 



Lat 



Long 



Date Gear 



BRAZIL BASIN 



Atlantis II 162 

 31 



1493 1 



08"02.2'S 



34tj3.0'W 



19.2.67 ES 



The type specimen has been examined by us. 



Distribution. An upper slope species previously recorded only 

 from the Gulf of Mexico but here found in the Brazil Basin. It occurs 

 at depths from 347m to 1493m. 



Shell description (Fig. 1 1 ) 



Dall (1881) gave an adequate description which was later (Dall, 

 1886) augmented by good internal and external lateral views of the 

 shell. The specimen collected from the Brazil basin differs little 

 from the type (Dall, 1881, 1886)(Fig. 11):- 



Shell elongate, solid, oval, ornamentated with concentric ridges; 

 umbo not particularly large or elevated, somewhat anterior to the 

 mid line; postero-dorsal margin almost straight, slightly upturned 

 posterior to the distal limit of the hinge, then sharply and smoothly 

 curved to posterior margin, ventral margin shallow smooth curve, 

 not posteriorly sinuous, anterior margin smoothly curved, antero- 

 dorsal margin relatively steeply angled, distally slightly raised; 

 hinge plate elongate, relatively wide, hinge teeth chevron-shaped, 9 

 in anterior and 12 in posterior series; external ligament slightly 

 opisthodetic, short; resilium small ventral to umbo. 



Dall (1881) states that there are an equal number of teeth in the 

 anterior and posterior series (15). however the type specimen which 

 is larger than the present specimen, has 17 anterior and 20 posterior 

 teeth. 



The total length of present specimen is 3.1mm. 



Internal morphology 



Both adductor muscles are oval in cross section, the anterior is 

 somewhat larger than the posterior but neither is particulaly large. 

 The foot is relatively short with large marginal papillae. The palps 

 are relatively short with 7 broad internal ridges. The gill is also short. 

 The siphonal embayment is shallow and the siphons similar to those 

 described for N. salicensis. The hind gut forms a single loop to the 

 right side of the body and has a typhlosole along its entire length. 



Neilonella whoii new species 



Type specimen. 

 1995053. 



Holotype BMNH 1995052; paratypes BMNH 





