21 117 
Byssoarca pusilla, SowrErBy, Proc. Zool. Soc., I, 18338, p. 18. 
Arca — — Reeve, Conchol. icon., I, Arca, Sp. 112. 
— donaciformis, REEvrE, Conchol. icon., Il, Arca, Sp. 104. 
—  (Byssoarca) pholadiformis, C. B. Apams, Shells coll. at Panama, 1852, p. 260. 
Barbatia (Acar) laminata, ANGAS, Proc. Zool. Soc., 1865, pp. 697 and 655. 
Arca (Byssoarca) dubia, Baird, BReENCHLEY, Jottings during the cruise of H. M. S. Curacoa among the 
South Sea Islands, 1873, p. 453, pl. 42, figs. 5—6. 
— M Coy1, Tenison-Woops, Transact. and Proc. Roy. Soc. Victoria, vol. XIV, 1878, p. 61. 
Gulf of Siam (‘/2). 
Long. 15 mm. 
Distribution: — Gulf of Manaar, Mangalore (Malabar Coast), Maldive Archip., 
Arabian Sea, Gulf of Oman, Persian Gulf, Gulf of Aden, Red Sea, Gulf of Suez, 
Mozambique, Natal coast, Seychelles, Amirantes, Madagascar, Mauritius, Cape of 
Good Hope, St. Helena, Ascension, Annobon, St. Thomé, Cape Verd Isls., Madeira. — 
Tonkin, South Japan, Philippines, Moluccas, Torres Strait, North, East and South 
Australia, Tasmania, the South Sea Islands, New Caledonia. — West coast of America 
from St. Barbara to Peru; East coast of America: Bermudas, Florida, Gulf of Mexico, 
Bahamas, Greater and Lesser Antilles. 
The wide distribution of this species, together with its great tendency to varia- 
tion, has caused it to have numerous names given to it in the course of time. 
LiscHkE,' and more recently Ep. Lamy,’ have recorded a great many of these. 
A. H. Cooke*® doubts the correctness of LiscHke’s views upon the identity of these 
species; he is of opinion that they are three well-distinguished forms: gradata (the 
West American form), Domingensis -|- squamosa (the West Indian form), divaricata, 
Sow. = plicata, Ch. (the East Indian form); but the distinguishing characters 
recorded by him are not valid. I have at my disposal a fairly large quantity of 
material of A. Domingensis from the West Indies, and the extensive variation-series 
includes, as far as I can see, all the forms which have been established. I think, 
W.H. Dati is mistaken when he?* refers A. Domingensis, Lam., and gradata, Brod. & 
Sow., from the Gulf of Mexico and the Caribbean Sea to A. reticulata, Ch. He sup- 
poses that A. congenita, Edg. A. Smith, also, is possibly only a form of A. plicata, Ch. 
Arca (Acar) tenella, Reeve. 
(Pl. 1, Figs. 11—13). 
Arca tenella, Reeve, Proc. Zool. Soc. London, XII, 1844, p. 124. 
— _ —  Conchol. icon., ], 1844, Arca, Sp. 91. 
— (Barbatia) tenella, Reeve, Marrint u. CHEMNitz, Conchyl. Cabin., VIL, 2 Abth., p. 155, pl. 39, figs. 5—6. 
Barbatia mollis, DuNkER, Novitates concholog., 1867, p. 92, pl. 31, figs. 2—4. 
Arca (Barbatia) mollis, DuNkeR, MArrini u. CHEMNITZ, Conchyl. Cabin., VII, 2 Abth., p. 128, pl. 33, figs. 5—6. 
— (Acar) tenella, Reeve, Lamy, Journ. de Conchyl., vol. 55, 1907, p. 93. 
' Japanische Meeres-Conchylien, II, p, 142, II, p. 107. 
* Journal de Conchyliologie, vol. 52, 1904, pp. 142—47, and vol. 55, 1907, pp. 80—87. 
5 Annals and Magazine of Nat. Hist., 5. Ser., vol. 18, 1886, p. 94. 
* Report of the Mollusca of the “Blake” Expedition, I, 1886, p. 242. 
