ZOOLOGY OF FERNANDO NORONHA. 
499 
50. Mytilus exustus {Lamarck) , Beeve. 
This is a "West- Indian species, and was also obtained by the 
‘ C-ballenger ’ expedition at Fernando Nor on ha and Pernambuco*. 
51. Arca imbricata, Bruguiere . 
This species was also obtained by the £ Challenger’ Expedition 
at Fernando 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 (Acar) Adamsii, Shuttleworth, MS.?. — Arca Adamsi 
in Cuming's Collection. (Plate XXX. figs. 6, 6 a.) 
Testa oblonga, snbqnadrata, sordicle albida, insequilateralis, 
antice curvata, postice oblique arcuata, interne in medio levissime 
sinnata, lineis elevatis radiantibus aliisque concentricis cancel- 
lata ; umbones parvi, parum remoti, panlo 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. 7j, diam. 7\. 
Hab. 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 of 
the above-named species. The muscular impressions are clearly 
defined by a raised ridge which is continued upward towards the 
umbones. 
53. Lima squamosa, Lamarck , var. 
Hab. Atlantic, Pacific, and Indian Oceans. 
The distribution of this species is given in my Report upon the 
‘ Challenger ’ Pelecypoda. The specimens from Fernando No- 
ronha seem intermediate between L. squamosa and L. multi- 
costata, having fewer ribs than the latter, and more than typical 
examples of the former. 
A specimen 22 millim. long lias twenty-six ribs, and another 
example 1G millim. in length has but twenty-one. 
* Vide 1 Report on ‘ Challenger ’ Lamellibranchiata, p. 272. 
