| OCR Text |
Show 538 REV. T. R. R. STEBBING ON CRUSTACEANS [May 22, wholly uncovered, digitiform-arborescent branchiae, these being partially covered in the Lophogastridae and Eucopiidae, wanting in the Mysidae, and not arborescent in Anaspides. Gen. EUPHAUSIA Dana. 1852. Euphausia, Dana, U.S. Expl. Exp. vol. xiii., Crust, pp. 637, 639. 1863. Euphausia, Claus, Zeitschr. fiir wiss. Zool. vol. xiii. pt. 3, p. 442. 1876. Euphausia, Claus, Geuealog. Grundlage des Crustaceeu- Systems, p. 7. 1883. Euphausia, Sars, Christiania Vidensk.-Selsk. Forh. no. 7, p. 11. 1885. Euphausia, Sars, ' Challenger' Schizopoda, Eeports, vol. xiii. p. 63. 1893. Euphausia,Ortmann, Decapoden u. Schizopoden, Plankton- Exp. vol. ii. p. 10. This genus is distinguished from others in the same family by having tbe last two pairs of trunk-legs (that is, the fourth and fifth peraeopods) rudimentary, except in regard to the branchiae, which are strongly developed. The beautiful and elaborate figures with which Sars has illustrated this genus refer to a form which he calls Euphausia pellucida Dana. His reason for choosing the name is that so common a form cannot reasonably be supposed to have escaped the attention of Dana, and that of the four species described by Dana the one named pellucida seems to agree with it best. Against this reasoning there is much to be urged. Sars speaks of " the specimens examined by Dana;" but Dana's description would rather lead one to suppose that he had only at command a single specimen, of the female sex. A single specimen resulting from a four years' voyage may just as well belong to a rare species as to a common one. Dana's descriptions in some cases are, as Sars observes, anything but satisfactory. They are sometimes inconsistent one with another and with the figures to which they refer. In his account, for example, of E. pellucida he says that the last three joints of the feet are together nearly twice as short as the preceding joint. This is not borne out by his detail-figure even of the " posterior thoracic leg," and is still less likely to be true of the preceding feet. It is very far from true of any of the feet in the form described by Sars ; but this is separated from Dana's by other characters. Dana describes each of his species as " brevissime ros-tratus," and it is difficult to suppose that he could have overlooked such a difference in the length of the rostrum as exists between the forms named by Sars respectively E. pellucida Dana and E. splendens Dana, the rostrum in the former reaching to the distal end of the eyes, and in the latter " scarcely projecting bevond the ocular segment." The pellucida of Sars is distinguished by the great length of the denticulate basal spine of the second antennae, this spine being short in Dana's detail-figure. In pel- |
