348 On the Crustacea of St. Andrews. 



laminarlan region. Occasionally used as bait. Swarms in 

 tlie zoea-stage occur in autumn at the surface of the water in 

 the bay ; they are almost invisible with the exception of the 

 greenish-blue eyes. 



This crustacean has nine branchife : — the first rudimentary, 

 and attached to the horizontal portion of the first pair of foot- 

 jaws ; the succeeding, rather long and delicate organs, fixed 

 to the second pair of foot-jaws on opposite sides of the hori- 

 zontal portion ; while six are attached to the body of the 

 animal, four being prominent, as in allied forms. The flabel- 

 lum of the first pair passes between the four prominent and 

 larger branchige and the apodematous region, so as to sweep 

 their inner surface ; while the same organ of the second pair 

 goes between the same portion of the shell and the fifth and 

 sixth branchise (counting from behind), and may also affect 

 the exposed surface of the seventh, which lies in the groove 

 anteriorly. The long and finely curved flabellum of the third 

 pair of foot-jaws curves externally, so as to brush all the 

 seven. The great development of this organ, its central cal- 

 careous bow, and long hairs are thus explained. The branchial 

 lamina are an-anged with their edges to the afferent current, 

 which crosses the organs at right angles to their long axes, and 

 so impinges between the plates. The action of the broad 

 shield of the fourth pair of foot-jaws, again, affects the ingoing 

 stream, and plays upon the large flat surface at the base of 

 the flabellum of the third pair. It would tend thus to spread 

 out the long hairs of the latter, and direct the current upwards 

 over the branchial laminae. The fifth pair as a whole would 

 seem to be connected with the buccal rather than the respira- 

 tory apparatus; for the curiously twisted portion (c, fig. 6, Trans. 

 Linn. Soc. vol. xxiv. p. 88) is nicely adapted to the deep an- 

 terior notch of the mandible, while the curved portion (a) enters 

 the mouth above the chitinous tissue filling up the posterior 

 notch of the mandible. The tuft of long hairs (e, loc. cit.), 

 however, may render some assistance to the branchial portion 

 of the fourth pair of foot-jaws in contact with it. 



The appendage of the mandible (a, fig. 7, o/?. cit.) seems to 

 have a considerable influence in the prehension and direction 

 of the food between the maxillre ; it has lateral motion as 

 well as flexion and extension. The flexible process filling up 

 the gap in the underpart of the maxilla, and connected with 

 the lip beneath the latter, would seem to prevent the escape of 

 particles in biting and deglutition. It is attached to a firm 

 horny basis, which has free horizontal, but little or no vertical 

 motion, except when greatly extended. 



In females bearing eggs the muscles on the external or 



