202 eeport— 1878. 



bud, supporting at its apex a crown of auditory cilia, and one short ciliated 

 hair. 



The second antenna?, c, c, consist of a peduncular basal joint, supporting 

 two branches ; the internal gradually narrows from the base, and termi- 

 nates in a long spine-like hair fringed with cilia ; the external is in the 

 form of a squamose plate, the external margin of which is straight, and 

 the internal becoming broader from the base, and then rapidly running 

 to an apex ; the inner oblique distal margin being fringed with ciliated 

 hairs. The mandible and oral appendages are well formed, each assuming 

 an approximation to the adult condition, except the posterior, or tetarto- 

 gnathus, which assimilates to that of the gnathopoda, the character of 

 which it partakes. In each, the number of joints in the primary ramus 

 has increased to six, and the pereiopoda exhibit evidence of rapid develop- 

 ment, in the form of cylindrical pendulous sacs, which decrease in length 

 posteriorly. 



There are slight variations from this form in different genera. 



In Palccmon the primary branch of the gnathopoda have but four 

 joints, and terminate in stiff short spine-like hairs ; while in Crangon the 

 hairs are long, flexible, and ciliated. This latter is the case with the 

 zosea of Alpheus and Stenopus; while in that of Hymenocera the character 

 is more in accordance with Palcemou. 



The zosea in these orders respectively, Brachyura, Anomura, and 

 Macrura, while they differ from each other, yet possess characters that 

 are generally common to two. The form of the carapace in the zosea of 

 the Brachyura, with its great dorsal spine, which although in some genera, 

 as Gelassimus, Libinea, and Mencetheus, it is much reduced, so that in the 

 last it is a mere prominence, is still a feature peculiarly chai'acteristic of 

 the zosea of the order. Next to which are the great sjnnes on the lateral 

 walls of the carapace. The presence of these is not so constant, but they are 

 never seen on the carapace of any zosea in either of the other two orders. 



In the Anomura great lateral spines, and sometimes smaller spines, 

 project from the posterior margin of the carapace ; these, together with 

 the rostrum, more or less important, is a feature peculiar to this order, 

 and from my own knowledge I am not aware of any exception to this 

 rule. But Claus, in his work so frequently quoted, has given the figure 

 of one that has all the characters of the zoaea of the Anomura ; but he calls 

 it an " Erichthina larva" (PI. IV., fig. 1), but adds, " Nach Willemoes- 

 Suhm die Larva von Leucifer ; " but certainly it bears no resemblance to 

 the young Erichthina as it quits the ovum of the adult Squilla. Another 

 feature that especially belongs to the zoaea is that of the terminal somite 

 of the pleon, or telson. It is always forked in the Brachyura, and the 

 few cases in which the terminal spines are short, still retain a distinct 

 and characteristic feature of the group. 



In the zosea of the Macrura the carapace is free from spines or processes, 

 and the terminal somite is flattened out into a broad thin fan-like plate, 

 divided in the median line by a more or less defined emargination. 



Now, if we compare the zosea of the Anomoura with these two 

 groups, we shall find that the tendency is to class them from their general 

 form with the zoaea of the Macrura. And this, without exception, includes 

 the Porcellanidae, Dromidse, and other depressed forms, as well as the 

 Paguridae. And the stage in development of the antennae exhibits an ap- 

 proximation to the Brachyura zoaea only in the first pair, while in all 

 the other appendages the Macrura features prevail. 



