. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) 105. Fig. 4. Neilonella salicensis. A series of shells, from Atlantis II station 73 from the North Atlantic Basin, in lateral view from right side to show change in shape with increasing size. Scale = 1mm. Shell description (Figs 2-4) Shell robust, moderately elongate, moderately wide, ornamented with concentric ridges sometimes in groups of three to four well- defined ridges alternating with two to to three slighty less well-defined ridges slightly wider spaced than the former, light to dark straw-coloured per
. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) 105. Fig. 4. Neilonella salicensis. A series of shells, from Atlantis II station 73 from the North Atlantic Basin, in lateral view from right side to show change in shape with increasing size. Scale = 1mm. Shell description (Figs 2-4) Shell robust, moderately elongate, moderately wide, ornamented with concentric ridges sometimes in groups of three to four well- defined ridges alternating with two to to three slighty less well-defined ridges slightly wider spaced than the former, light to dark straw-coloured periostracum; umbos moderately prominant, somewhat anterior to mid-line (postumbonal length of total length), inward and slightly anterior facing; dorsal shell margins deep set close to umbo but no lunule or true escutcheon, antero- dorsal margin slopes down to join anterior and ventral margins in smooth curve, postero-dorsal margin almost straight, may be slightly angled at posterior limit of hinge short of acutely rounded posterior margin; posterior limit of shell somewhat dorsal to mid horizontal line, anterior limit of shell at mid line; posterior margin of smaller specimens less acutely rounded; hinge plates elongate, moderately broad, increasing slightly in width distally, anterior and posterior hinge teeth series meet below umbo with no edentu- lous space between, teeth numerous, up to 19 in posterior series and 14 in anterior series depending on size of specimen, obtuse chevron-shape, proximal hinge teeth very small, those more distal elongate and so closely articulated that it maybe impossible to separate valves without damage to them; internal ligament (resilium) microscopic, present ventral to umbo at outer margin of hinge plate, external ligament opisthodetic, relatively short, short anterior part present. Maximum total length of present specimens As in most deep-sea protobranchs, there is a change in the shape of the shell outline as growth occurs (Figs 4
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