52 



in the north, along the Philippines, Sunda Islands, Moluccos, New Caledonia, Australia to New 

 Zealand and South Sea Islands. 



In the "Siboga" collection A. [A.) plicata is represented by a fair number of stray valve, 

 collected at Sailus Ketjil, Paternoster Islands (St. 37), Bay of Bima (St. 47), Sapeh Strait (St. 49^), 

 Western entrance of Samau Strait (St. 59), Bornéo Bank (St. 80), St. 90 (i°i7'.5 N., ii8°53'E.), 

 St. 95 (5°43'.5 N., ii9°4o'E.), St. 105 (6°8'N., i2i°i9'E.), Anchorage off Kilsuin, West 

 Coast of Kur Island (St. 250), and Anchorage off Sailus Besar, Paternoster Islands (St. 315). 

 The largest spécimen is a left valve from St. 49^, with the measurements as foUows : ^ — 

 Length 28 mm., height 13.8 mm., diameter of single valve 5 mm. 



2. Arca {^Acar^ incerta Smith. 



1899. Arca [Barbatià] incerta Smith, Ann. Mag. Nat. Hist., (7) IV, p. 251. 



1901. Arca [Barbatià) incerta Smith, Illustr. Zool. "Investigator", pi. XIII, figs. 3, 3^. 



1904. Arca [Barbatià] incerta Smith, Ann. Mag. Nat. Hist., (7) XIV, p. 12. 



1906. Arca [Barbatià] incerta Smith, Ann. Mag. Nat. Hist., (7) XVIII, p. 253. 



1907. Arca [Acar] incerta Lamy, Journ. Conchyliol. LV, p. 96. 



191 1. Arca incerta Pelseneer, "Siboga" LamelHbranches (Anat.), pp. 9, 13, 15. 



This species though superficially resembling A. scabra Poli and A. nodtilosa Millier, is 

 certainly distinct from either. Smitii placed A. incerta in the subgenus Barbatià Gray, but the 

 greatly trellised sculpture, the subcarinated posterior margin and the ligament not reaching up 

 to the umbones leave no doubt about its being a true Acar Gray. 



Distribution : — The species was described from shells obtained at depths of over 400 

 fathoms from round the coasts of Peninsular India — from OffTravancore and in the Gulf of Manaar. 



In the "Siboga" collection it is represented by young shells from Bay of Nangamessi, Sumba 

 (St. 53), Bank between islands of Bahuluwang, and Tambolungan, South of Saleyer (St. 66), St. 88 

 (Deep Sea trawl at o°34'.6N., ii9°8'.5E), St. 90 (281 mètres 1° 17^.5 N., ii8°53'E.), St. 94 

 (5° I i'.2 N., I 19° 35^.4 E. 450 mètres). St. 98 (350 mètres, 6°9' N., 120° 21' E.), St. 105 (275 mètres, 

 6°8'N., 121° 19' E.), St. 170 (Deep-sea trawl, 3°37'.7S., i3i°26'.4E. 924 mètres), St. 221 

 (Deep-sea trawl, 6° 24' S., 124° 39' E. 2798 mètres). St. 251 (204 mètres, 5° 28^.4 S., i32°o'.2 E.), 

 St. 256 (397 mètres, 5° 26^.6 S., i 32° 32^.5 E.), St. 259 (487 mètres, 5° 29^.2 S., i 32° 52^.5 E.), 

 St. 260 (5°36'.5S., i32°55'.2E. 90 mètres), St. 262 (5°53'.8S., i32°48'.8E. 560 mètres) and 

 Macassar. 



3. Arca (Acar) tenella Reeve. 



1844. Arca tenella Reeve, Conch. Icon., II, Arca, pi. XIV, fig. 91. 



1844. Arca tenella Reeve, Proc. Zool. Soc. London, p. 124. 



1845. Arca tenella Catlow & Reeve, Conch. Nomencl., p. 51. 

 1848. Arca tenella Nyst, Mém. Soc. Roy. Belgique, XXII, p. 72. 



1857. Arca Barbatià tenella Adams, H. & A., Gen. Rec. Moll., II, p. 535. 



1860. Arca tenella Reeve, Elem. Conch., II, p. 93. 



1867. Barbatià mollis Dunker, Novitat. Conch. Moll. Mar., p. 92, pi. XXXI, figs. 2—4. 



1869. Barbatià mollis Dunker, Cat. Mus. Godeffroy, IV, p. 114. 



1874. Barbatià tenella Dunker, Cat. Mus. Godefifroy, V, p. 174. 



1877. Barbatià tenella Tapparone-Canefri, Ann. Mus. Civ. Stor. Nat. Genova, IX, p. 292. 



1880. Arca [Barbatià] tenella von Martens, Mobius Beitràg. Meeresf. Mauritius, Seychell. p. 320. 



