The Indian bird erroneously called _Pitta thoracica_ by M. Temminck, follows this in close affinity, and is either the Grallatorial type, or the immediate point of connection between _Malacocircus_ Sw. and _Timalia_ Horsf. Total length 9 inches; bill from the gape 1-1/10; wings 4; tail 3; tarsus 1¾; hind toe and claw 1½. * * * * * * [Illustration: BYSSOARCA _Zebra_.] BYSSOARCA Zebra. _Zebra Ark-shell._ ---- Genus. Arca. _Lin. Lam._ Sub-genus. Byssoarca. _Nob._ ---- SUB-GENERIC CHARACTER. _Animal_ fixed by byssiform filaments to other bodies. _Shell_ transverse; umbones remote; valves gaping in the middle of the ventral margin. ---- SPECIFIC CHARACTER. _Margins angulated; valves marked with simple uniform and regular grooves, radiating from the umbones: shell transversely and obliquely striped with brown._ ---- It is somewhat surprising that the sedentary type of the genus _Arca_ should have been so long uncharacterized in our Conchological Systems; seeing that the other four types, viz. _Arca_, _Pectunculus_, _Cuculloea_, and _Nucula_, were defined many years ago by the celebrated Lamarck. We have consequently supplied this omission; and at the same time have selected a species hitherto, we believe, confounded with the _B. Noæ_; from which it differs in sculpture, colour, and in the umbones being less remote from each other. The Animals of these shells affix themselves to other bodies by a particular muscle, which is protruded through the gaping part of the valves; they also adhere, when young, by the byssiform epidermes which covers the exterior: a specimen now before us, which we procured in the Bay of Naples, perfectly exemplifies this singular property. The present species is not uncommon in the West Indies, and has been sent to us from Jamaica. Like all others of this particular type it is almost constantly covered by coralline substances. * * * * * * [Illustration: APALIS _thoracica_. _Gorget Warbler._] APALIS thoracica, _Gorget Warbler_. ---- Family Sylviadæ. Sub-fam: Sylvianæ. Genus (?) Apalis. GENERIC (?) CHARACTER. General structure of _Prinea_, but the bill shorter, the plumage more compact, and the outer toe not connected to the middle as far as the first joint. ---- SPECIFIC CHARACTER. _Olive green, beneath yellowish white; breast with a black collar; three lateral tail-feathers partly white: front black._ Le Plastron Noir. _Le Vaill. Ois. d'Af. 3 pl. 123. f. 1. male. 2. fem._ Motacilla thoracica. _Nat. Miss. 22. pl. 969._ ----