ZOOLOGY OF FERNANDO NORONHA. 499 



50. Mttilus exustus {Lamarck), Beeve. 



This is a West-Indian species, and was also obtained by the 

 ' Challenger ' expedition at Fernando Norouha and Pernambnco*. 



51. Arca imbricata, Brugnicre. 



This species was also obtained by the ' Challenger' Expedition 

 at Fernando Noronlia ; and other examples were dredged near 

 Cape York, N. Australia. This seems a remarkable distribution ; 

 still, as far as I can discover, there appears to be no differ- 

 ence in the shells. 



52. Arca (Agar) Adamsii, Shift! ewortJi, 318.?. — Arca Adamsi 

 in Cuming^s Collection. (Plate XXX. figs. 6, 6 a.) 



Testa oblonga, subquadrata, sordide albida, iusequilateralis, 

 antice curvata, postice obliqne arcuata, iuferne in medio levissime 

 sinuata, lineis elevatis radiantibus aliisque coucentricis cancel- 

 lata ; umboncs parvi, parum renioti, paulo ante medium collocati ; 

 area dorsalis angnsta, utrinque acuminata; ligamentum mini- 

 mum, adamautiforme, transversim stinatum ; pagina interna 

 alba, radiatim plus minus t^ubstriata. 

 Longit. 12 millim., alt. 7^, diam. 7-fr. 



Hah. St. Vincents, Jamaica, and St. Thomas {Brit. Mus.). 

 Two specimens bearing the above name occur in Cuming's 

 collection, and others from Jamaica presented by Dr. P. P. 

 Carpenter are also similarly labelled ; but I have not succeeded 

 in finding any description by Shuttleworth of this species. 



It is closely related to A. lactea, Linn., A. solida, Sowerby, and 

 some others. The points of contact of the radiating and con- 

 centric lirse are nodulous, and a little coarser than in either o£ 

 the above-named species. The muscular impressions are clearly 

 defined by a raised ridge which is continued u])ward towards the 

 umbones. 



53. Lima squamosa, LamarcJc, var. 



Hal. Atlantic, Pacific, and Indian Oceans. 



The distribution of this species is given in my Report upon tlie 

 ' Challenger ' Pelecypoda. The specimens from Fernando No- 

 ronha seem intermediate between L. squamosa and L. onulti- 

 costata, having fewer ribs than the latter, and moi'e than typical 

 examples of the former. 



A specimen 22 millim. long has twenty-six ribs, and another 

 example 16 uiillim. in length has but twenty-one. 



* Vide ' Repoi't on ' Challenger ' Lamellibranchiata, p. 272. 



