que testaceo croceo-testaceo sordido variegatis; oculorum pupillæ nigrescentes: abdomine elongato augusto coarctato, segmentis postice, atris.

Longitudo 0055 millemetrorum.

Habitat in mari Atlantico; fuco natanti adhærens.

U. With the thorax, antennæ, eyes, pedipalpi, feet and abdomen testaceous variagated with dusky saffron testaceous, jet black; the pupil of the eyes blackish; the abdomen elongated narrow contracted; the segments behind black.

Length 2 inches.

Inhabits the Atlantic, adhering to fucus natans.

2. Usterocheirus Brachypocoilion.

U. Thorace, antennisque brunneis; pedibus abdomineque pallidioribus; abdomine brevissimo latissimo.

Longitudo 0029 millemetrorum.

Habitat cum præcedente.

U. With the thorax and antennæ brown; the feet and abdomen paler; the abdomen very short and very broad.

Length 13-12 of an inch.

Found with the preceding.

Zuphanusa.

Antennæ quatuor, elongata trifida, multi articulatæ ; apice externe ciliata; filamentum inferius, superiore longiore

interne ciliatum, exteriores basi filiformi; lamella ovata compressa ciliata, terminati; filamentula ad basin externe instructa.

Pedum paria duo antica mono-dactylo anteriore minore augustiose paria tria postica, æquales anguibus arcuatis instructa.

Antennæ four elongated, trifid, many-jointed, with the apex externally ciliated; external ones with a filiform base terminated with an ovate compressed ciliated lamella, furnished at its base externally with a very minute filament.

Zuphanusa Smithiana.

Z. Thorace antennis, oculorum pedunculo, pedibus abdomineque hyalino, ocraceo florescentibus.

Longitudo 0054 millemetrorum.

Habitat in mari Atlantico, fuco natanti adhærens.

Z. With the thorax, antennæ peduncles of the eyes, feet and abdomen and hyaline, ochre yellowish.

Length 2 inches.

Inhabits the Atlantic ocean adhering to fucus natans.

ON THE GENUS MEGALOPHTHALMUS, A NEW AND VERY INTERESTING GENUS, COMPLETELY PROVING THE THEORY OF JULES-CÆSAR SAVIGNY TO BE CORRECT; BY WILLIAM ELFORD LEACH, M. D. F. R. S. &c. HONORARY MEMBER OF THE PLYMOUTH INSTITUTION.

MEGALOPHTHALMUS.

Antennæ omnino fere ut in genere Palamonide.

Oculi, maximi subglobosi; pupillæ reticulatæ.

Pedum, paria prima, secunda, tertia, quarta, quinta et sexta, consimilia natatoria; par septimum stirpe interne compressa plus complicata; pedipalpum fere verum efformans; par nonum stirpe interna compressum pedipalpum verum efformat; stirpe externa brevissima apice bifida.

Lamellæ caudales valda inæquales.

Antennæ resembling in almost all respects the genus Palamon.

Eyes very large; subglobose, the pupils reticulated.

Feet; the first, second, third, fourth, fifth and sixth pair alike in form and size, and formed for swimming; the seventh pair with the internal footstalk compressed, half formed into

a pedipalpus; the eighth pair with the external stirps compressed, more complicated, forming almost a true pedipalpus; the external footstalk is very short, with its apex very short and bifid.

Caudal lamellæ very unequal.

Megalophthalmus Fabricianus.

M. totus hyalinus fulvescens; oculorum pupillis aterrimis; abdominis segmentis supra stellatim sculptis.

Longitudo 0015 millemetrorum. .

Cancer pedatus, Othonis Fabricii, Faun. Græn. 243, No. 221.

Habitat in mari Boreali vulgatissimus.

M. wholly hyaline fulvescent; the pupil of the eyes jet black; the abdominal segments sculptured with striæ forming

a star.

Length 7-92 of an inch.

Found abundantly in the nothern seas, especially on the coast of Greenland, and in Baffin's bay.

I will now shew how the genus Megalophthalmus explains the theory of Savigny, respecting the various functions performed by the eighteen pair of legs, which he affirms, belong to all the genera of the Crustacea Malacostraca Pedophthalmia.

In the majority of the genera the five anterior pairs of feet perform the offices of locomotion, or of prehension; and the

Y

four hinder pairs, those of manducation or of carrying the food to the mouth; which in all the genera is furnished with two hard testaceous jaws.

This is the only genus in which the three pairs before the five hinder pairs perform the functions of locomotion; the change in the three hinder ones, from the five pair of the hinder ones is so gradual, that his theory is in my opinion satisfactorily established; and may in all probability be more fully so, by the discovery of some genus that has not yet been observed. I again state from my own observation, that I think his theory stands on a fair base, and wants but little (if any thing,) to confirm it.