RHYNCHONELLA. 
Puate I. 
Genus RHYNCHONELLA, Fischer. 
Testa inequivalvis, subglobosa, impunctata, nunc levigata, 
nunc radiatim striata vel costata, valvd ventrali acute 
rostrata, rostro incurvo, subtus perforato, perforatione 
interdum tubulari, deltidio integro, interdum amplo, 
oblongo-quadrato, deltidio perangusto, laté partito ; 
valvé dorsali laminis duabus angustis curvatis ad car- 
dinem munité, denticulis duobus callosis sulcatis in 
valva oppositd interclausis. 
Shell inequivalve, subglobose, not punctured, sometimes 
smooth, sometimes radiately striated or ribbed, ven- 
tral valve sharply beaked, beak incurved, perforated 
beneath, perforation sometimes tubular, with the del- 
tidium entire, sometimes large, oblong-square, with 
the deltidium very narrow and widely separated ; 
dorsal valve provided with two narrow curved blades 
interlocking with two grooved callous denticles in 
the opposite valve. 
The well-known Parrot’s-beak of the Arctic Seas and 
its two recently discovered congeners from the antipodal 
region of New Zealand and the Feejees are chiefly inter- 
esting as being the only living representatives of a tribe 
of Brachiopods which existed in great abundance at the 
earliest period of the world’s history ; more than two 
hundred and fifty species being known in a fossil state 
from the very oldest Lower Silurian beds. The Rhyncho- 
nelle differ generically from the Terebratule in the follow- 
ing important particulars:—The animal has no apophy- 
sary skeleton for the support of its ciliary arms, but only 
a pair of hooked blades projecting from the hinge-margin 
of the dorsal valve. The arms are, moreover, disposed in 
six or seven free spiral gyrations, which are unfolded and 
protruded outwards or retracted at pleasure; and another 
characteristic feature of Rhynchonella is, that the shell is 
never punctured, as is invariably the case with Terebratula. 
The beak is more sharply hooked. In &. psittacea and 
nigricans the beak is incurved quite over the foramen, the 
foramen is large, and the deltidium is widely separated 
and almost obsolete; in 2. Grayi the foramen is terminal 
in the beak and the deltidium is entire. 
Species 1. (Fig. a, 4, Mus. Taylor; Fig. c, Mus. Cuming.) 
RHYNCHONELLA NIGRICANS. 
ovata, gibbosd, caruleo-nigricante, radiatim costatd, 
Rhyn. testa transversim 
costis subamplis, symmetricis, rostro parviusculo, mo- 
dice incurvo, foramine amplo, deltidio parviusculo, 
late partito. 
THE BLACKISH RHYNCHONELLA. Shell transversely ovate, 
gibbous, blue-black, radiately ribbed, ribs rather 
large, symmetrical, beak rather small, moderately in- 
curved, foramen large, deltidium rather small, widely 
separated. 
Terebratula nigricans, Sowerby, Thes. Conch, vol. i. p. 
342. pl. 71. f. 81, 82. 
Rhynchonella nigricans, Davidson. 
Hab. New Zealand (dredged at Faveau Strait, about five 
miles north-east of Ruapuke Island, in nineteen fa- 
thoms, off coral rock); Evans. 
A most interesting species, of which several specimens 
are now known, all distinguished by the same gibbous 
transversely ovate form and symmetrical ribbing. 
Species 2. (Fig. a, 6, c, Mus. Cuming.) 
RHYNCHONELLA PSITTACEA. Rhyn. testd subtrigono-glo- 
bos, olivaceo-nigrad, radiatim subtilissimé lineari-sul- 
catdé, rostro acutissimé incurvo, foramen elongato- 
quadrato, deltidio angusto, laté partito, valvd dorsali 
conspicué globoso-inflatd, ventrali planiusculd, medio 
flexuoso-canaliculata. 
THE PARROT’S-BEAK RHYNCHONELLA. Shell somewhat 
triangularly globose, olive-black, radiately very finely 
linearly grooved, beak very sharply incurved, foramen 
elongately square, deltidium narrow, widely sepa- 
rated, dorsal valve conspicuously globosely inflated, 
ventral rather flat, flexuously channelled in the 
middle. 
Anomia rostrum-psittacei, Chemnitz, Conch. Cab. vol. viii. 
p. 106. pl. 78. f. 7138 a, 4, ¢. 
Le Bec de Perroquet, D’ Argenville. 
Anonia psittacea, Gmelin. 
Terebratula psittacea, Lamarck. 
Hypothyris psittacea, King. 
Rhynchonella psittacea, Fischer. 
Gypidia psittacea, Menke. 
Lampas psittacea, Gray. 
Hab. Boreal and Arctic Seas (from low-water to a depth 
of a hundred fathoms). 
This well-known species is a native of the Arctic rather 
February, 1861. 
