22 



A.V. SYSOEV 



The species is rather variable in the shell proportions: the shell 

 may be elongated (Fig. 94) and very similar to the holotype 

 figured by Kilburn (1986), or more stout and broad (Figs 95 & 

 96). The H/D ratio varies from 2.03 to 2.55 (2.44 in the 

 holotype). The prominence of the columellar pleat can also vary 

 up to almost complete absence. However, there are rather 

 constant features which are characteristic of the species and 

 distinguish it from B. fissa (see below). These are a strongly 

 projecting peripheral keel, distant primary spiral cords with a 

 thin secondary rib in most interspaces, and low position of the 

 peripheral keel, which is bordered or almost bordered by a 

 deeply channelled suture even on the last spire whorls. The 

 protoconch is similar to that of B. oldhami. Radular teeth are 

 typical for the subgenus, awl-shaped, curved, and rather short. 

 The mean tooth length is 0.46 mm at H = 26.6 mm. The 

 operculum is small, oval, with subterminal nucleus. 



Distribution. Gulf of Aden and, probably, the Bay of Bengal, 

 528-1080 m. 



Bothy toma ( Parabathytoma) fissa (von Martens, 1901) 



Figs 9, 17 & 98-100 



Pleurotoma ( Dolichotoma) fissa von Martens, 1901, p. 18. 

 Genota ( Dolichotoma) fissa -von Martens, 1903 [1904], p. 87, pi. 

 1, fig. 14. 



Type locality. 'Valdivia', stn 264 (Somalia), 1079 m. 



Material, stn 176, 2 specimens and 12 shells. 



The species differs from B. regnans in having closely set spiral 

 cords, with almost equally strong granular secondary cords in 

 the interspaces, and less prominent peripheral keel which is 

 situated rather high on last spire whorls. The sutures are less 

 distinctly channelled than in B. regnans. The shell proportions 

 and the prominence of peripheral keel may vary (Figs 98-100). 

 There are one to three more or less developed columellar pleats; 

 usually two pleats are present and the upper one may be 

 subdivided into two by a groove. The radula and operculum are 

 similar to those of B. regnans. The mean tooth length is 0.5 1 mm 

 at H = 35.3 mm. 



Shells from an additional sample (R/V 'Akademik Mstislav 

 Keldysh', stn 1089, Tajoura Rift, Gulf of Aden, 857-900 m) 

 show the same characteristic features and the same range of 

 variability but are of larger size (up to 42.5 mm in height) and 

 possess 1 (usually) or 2 columellar pleats. 



Distribution. Somalia and Gulf of Aden, 665-1079 m. 



Genus TYPHLOMANGELIA G.O.Sars, 1878 



Type species: Pleurotoma nivale Loven, 1846 (monotypy) 



Typhlomangelia adenica Sysoev, new species 



Figs 4, 14 & 89 



Material, stn 26, 1 shell (paratype No. 1993106); stn 185, 2 

 specimens (holotype No. 1993104 and paratype No. 1993105). 



Description of holotype. The shell is small, broad, turreted, 

 solid, covered by thin light-brown periostracum, and consists of 

 4 remaining whorls. Protoconch and probably some upper 

 whorls are missing. The whorls are strongly angled at the 

 periphery, the subsutural slope is concave. There is a weak 



subsutural fold. Sutures are very shallow and indistinct. The 

 body whorl is large, and the shell base is weakly convex and not 

 differentiated from the canal. The axial sculpture consists of 

 numerous narrow oblique folds reaching the lower suture and 

 abruptly disappearing on the subsutural slope. The folds form 

 pointed tubercles just below the subsutural slope. On the body 

 whorl, they rapidly weaken downwards and do not reach the 

 shell base. There are 19 folds on the body whorl and 15 on the 

 penultimate. The subsutural slope is smooth except for growth 

 lines. A single spiral cord is situated on the subsutural fold, 2-4 

 cords are present below the subsutural slope on the spire whorls, 

 and there are about 1 5 low, widely and evenly spaced cords on 

 the body whorl, which become weaker towards the anterior end 

 and finally disappear. The aperture is oval, not differentiated 

 from the straight and short canal. The inner lip is covered with a 

 white callus which is thickened and becomes distinctly bordered 

 on the canal. The anal sinus is deep, broad and rounded, slightly 

 asymmetrical, its deepest point is situated just below the middle 

 of subsutural slope. H = 10.2, Hb = 6.6, Ha = 4.7, D = 5.6 mm. 



The paratypes are very similar to the holotype but smaller (H 

 = 7.7, D = 4.5 in paratype from stn 185 and H = 6.9, D = 4.1 in 

 paratype from stn 26). The operculum is rather large in 

 comparison to the aperture size, broadly leaf-shaped, with a 

 terminal nucleus. Radular teeth are typical of the genus, 

 awl-shaped, with short and straight shaft and relatively broad 

 base, 0.2 mm in length. 



The species differs from all other species of the genus in its 

 very small, broad shell, with a very short and straight canal. 



Distribution. Gulf of Aden, 2000-2312 m. 



Typhlomangelia maldivica Sysoev, new species 



Figs 6, 15 & 86-88 



Material, stn 143, 7 specimens (holotype No. 1993107 and 6 

 paratypes No. 1993108). 



Description of holotype. The shell is elongate fusiform, 

 slender, with a high spire, rather solid, covered with thin 

 grayish-brown periostracum, and consists of protoconch and 9 

 teleoconch whorls. The protoconch consists of about two 

 globose smooth whorls, the surface is partly eroded. Definitive 

 whorls are angled at the periphery, concave on the subsutural 

 slope, with distinct subsutural fold. The body whorl occupies 

 0.58 of the shell height, the shell base is weakly convex and 

 passes smoothly into the slightly twisted canal. The sutures are 

 distinctly channelled, especially in last whorls. The axial 

 sculpture consists of rounded folds below the subsutural slope; 

 they are most prominent and tuberculate in their uppermost 

 parts and weaken towards the lower suture. The folds tend to 

 become smoother on last spire whorls, and on the body whorl 

 they are very low and restricted to the whorl periphery. There are 

 13 folds on the body whorl and 12 on the penultimate. Spiral 

 sculpture is represented by rather strong and widely spaced 

 cords. One (or two on last whorls) strong cord is situated on the 

 subsutural slope, 1-3 cords are developed below the subsutural 

 slope of spire whorls (1 on initial whorls and 3 on the last one), 

 and about 20 cords cover the body whorl and the canal. On the 

 body whorl periphery, a weaker cord is situated in each 

 interspace between primary cords. The subsutural slope of the 

 initial whorls is smooth, but on subsequent whorls 1-5 thin 

 riblets are developed, with a stronger one in the centre of the 

 slope. The aperture is rather narrow, oval. The canal is 

 moderately long. The anal sinus is deep, rounded, slightly 



