. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) 71. Fig. 113 Yoldiella ella. Lateral view of a shell from the right side and a left valve to show detail of the hinge-plate. Specimens from Sta. INCAL OS 06. (Scale = mm). est shell height posterior to umbo; dorsal margin slightly convex, antero-dorsal anterior and ventral margins in a smooth continuous curve, postero-ventral margin rounded posteriorly, posterior margin in small specimens may have very slight, blunt, angulation, posterior limit slightly dorsal to horizontal midline, postero-dorsal margin cu
. Bulletin of the Natural History Museum Zoology. DEEP-SEA PROTOBRANCHIA (BIVALVIA) 71. Fig. 113 Yoldiella ella. Lateral view of a shell from the right side and a left valve to show detail of the hinge-plate. Specimens from Sta. INCAL OS 06. (Scale = mm). est shell height posterior to umbo; dorsal margin slightly convex, antero-dorsal anterior and ventral margins in a smooth continuous curve, postero-ventral margin rounded posteriorly, posterior margin in small specimens may have very slight, blunt, angulation, posterior limit slightly dorsal to horizontal midline, postero-dorsal margin curves gently from umbo to distal edge to hinge plate then slopes more acutely to posterior margin; hinge plate, long, characteristically angular below umbo, moderately broad proximally, narrow ventral to umbo, anterior and posterior ventral margins of hinge plate more or less straight, teeth strong, well-developed, equal number in anterior and posterior plates, up to 9 in specimen mm, ligament amphidetic, moderate in size, rectangular or slightly 'goblet'-shaped, short, wide, posterior external extension and long slender anterior external extension of fused periostracum. Prodissoconch length: 166 Maximum recorded shell length: mm. There is little change in the width/length or height/length ratios with increasing size, however, posterior umbonal i length increases slightly and the posterior margin becomes more smoothly curved. Internal morphology (Fig. 117). The anterior sense organ is well-developed. Posterior mantle fusion is minimal, ;limited to a fine bridge of tissue between the opposing inner mantle lobes forming a short exhalent siphon. The gill axis is attached laterally on either side of the bridge tissue. Ventral to it the inhalent siphon is reduced to a pair of unfused ithickened pads of tissue. The feeding aperture is poorly developed with a few gland cells present. Immediately ante- rior to the feeding aperture, the inner mantle fold is enlarged Fig. 114
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Keywords: ., bh, bookcentury1900, bookcollectionbiodiversity, bookleafnumber73
