| OCR Text |
Show 26 MR. R. GURXEY ox T H E [May 12, The basal part between the eyes is broad, and distally it contracts suddenly and tapers to a sharp point. In one example this narrow part was found to be bifid down to its base, though the postlarval form moulted from it was in no way abnormal. The general form of the carapace is unaltered. In the abdomen the laterodorsal spines of the fifth segment are longer, and end in a sharply down-curved hook. I have drawings of a larva taken in July 1901 at Plymouth, in which this spine is of an unusual length, being about two-thirds the length of the long sixth segment. The tail-plate, now distinctly separated from the sixth segment, is much narrower at the end compared with its total length, and its sides are not straight, but conspicuously curved. There are still seven seta? on each side of the posterior margin, but a short way up the side on either hand is a minute knob, representing the eighth seta found in other species. The antenna? (PI. Y I . fig. 14) are now still more elongated, the flagellum of the second antenna now considerably exceeding the scale in length. The latter has now a large number of marginal seta?. Such changes as have occurred in the maxilla? are unimportant. In the maxillipedes five joints can now be detected in the endo-podite of the second and third, but that of the first remains to all appearance three-jointed. All the thoracic appendages, as well as the pleopods, are now present, and have the usual Crangonid form. The first five pairs of thoracic appendages have exopodites. As regards the gills, not having any example of stage iv., 1 cannot offer any observations as to their origin, but in the last stage they are well developed, and the five posterior pairs are distinctly pleurobranchs. In this respect C. fasciatus and also C. trispinosus diner from C. vulgaris, in which Williamson describes the gills as having the position of arthrobranchs at this stage. The foregoing account shows that the larva of C. fasciatus is readily distinguishable from all other Crangon larvae yet described. The larva most closely approaching it seems to be one described by Clans (1861, taf. ii. fig. 1). This larva possibly may be that of C. sculptus, and differs from that now under consideration in its much more compact body and the relative length of its dorsal abdominal spines. The length of the antenna?, slender body, and shape and size of the abdominal spines are distinctive of the larva of C. fasciatus. The next moult leads at once to the postlarval stage, in which the adult form is assumed. The young shrimp has the broad, depressed form of the adult, with its characteristic square rostrum and bright, somewhat banded, colouring. The only important point of difference lies in the sculpturing of the carapace. In this first postlarval stage the carapace is smooth except for a short anterior median ridge, with two or three blunt prominences. |
