ZOOLOGY OF FERNANDO NORONHA. 



499 



50. Mytiltjs exustus {Lamarck), Reeve. 



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

 ' Challenger ' expedition at Fernando Noronlia and Pernambuco *. 



51. Arca imbricata, Bruguiere. 



This species was also obtained by the * Challenger' Expedition 

 at Eernando Noronha ; 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, Shuttle worth, MS.?. — Arca Adamsi 

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



Testa oblonga, subquadrata, sordide albida, iusequilateralis, 

 antice curvata, postice oblique arcuata, inferne in medio levissime 

 sinuata, lineis elevatis radiantibus aliisque concentricis cancel- 

 lata ; umbones parvi, parum remoti, paulo ante medium collocati ; 

 area dorsalis angusta, utrinque acuminata; ligamentum mini- 

 mum, adamantiforme, transversim striatum ; pagina interna 

 alba, radiatim plus minus substriata. 



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



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 lirae are nodulous, and a little coarser than in either of 

 the above-named species. The muscular impressions are clearly 

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

 umbones. 



58. Lima squamosa, Lamarck, var. 



Kab. Atlantic, Pacific, and Indian Oceans. 



The distribution of this species is given in my Eeport upon the 

 * Challenger ' Pelecypoda. The specimens from Fernando No- 

 ronha seem intermediate between L. sqimmosa and L. multi- 

 costata, having fewer ribs than the latter, and more than typical 

 examples of the former. 



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

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



* Vide ' Report on ' Challenger ' Lamellibranchiata, p. 272. 



