200 report — 1878. 



be taken as the type of zoasa. When it quits the ovum, and throws 

 off the enclosing membrane, and swims first as a free animal, it has a dis- 

 tinct and well-developed carapace. It is dorsally arched and laterally 

 compressed and rounded off at the infero-posterior angles. It is, moreover, 

 armed with long characteristic spines on the dorsal and lateral surfaces, 

 and anteriorly with a great rostrum, but these features vary in different 

 genera, as shown in PL VI., where the two extremes are seen. In Tra- 

 pezia, fig. 3, the spines are all very long, in Gelassimus, fig. 4, they are very 

 short. The pereion is in a compressed or immature condition, and the 

 pleon has six well-developed somites, the terminal one ending invariably 

 in a fork-like extremity that varies in degree, and is armed with a greater 

 or less number of strong stiff ciliated spines that differ in a constant degree 

 so as to enable one almost to define the generic limits of species. It has 

 invariably two pairs of antennas, represented by the early budding con- 

 dition of the permanent organ in the first pair, and by deciduous represen- 

 tatives in the second in the form of two long teeth or spines ; the 

 mandibles and two succeeding pairs of oral appendages ; the third pair, 

 or tetartognathus, being absent ; while the gnathopoda are developed into 

 large characteristic swimming appendages. Of these, which are invariably 

 biramose, one represents the permanent and the other the secondary branch 

 of the adult organ : in this early condition the primary or permanent branch 

 is five-jointed, and the second three. The number of these joints repre- 

 sents the more or less advanced condition of the zoaea, and corresponds 

 with the progressive development of the animal. The pereiopoda are 

 represented by two or three small sac-like lobes, within which the several 

 pairs may afterwards be seen to be developed. 



The brephalus of the Anomurais also a zoasa (PL VI., figs. 1 and 2), and 

 differs from that of the Brachyura more in general appearance than in its 

 degree of advanced development. The anterior portion corresponds, ex- 

 cept in the armature of the carapace, very closely with the same part 

 in the zoasa of the Brachyura, while the posterior portion of the animal 

 assimilates more nearly with that of the zoasa of the Macrura. 



If we take the zoaea of Pagurus as the type, we find that the carapace 

 is dorsally more depressed than in that of the Brachyura, and extends 

 nearly horizontally from the rostrum to the posterior margin of the cara- 

 pace, the lateral margins are not so deep, and are produced posteriorly, so 

 as to form a prominent process or tooth on each side. This projection is 

 very constant, but varies in degree with separate families. The rostrum 

 also is generally prominent, and projects horizontally forwards. 



The pereion is not appreciably developed. The pleon has six somites, 

 the posterior one being long, and terminating in a broad fan-like telson, 

 the posterior margin of which is divided into two halves by an excavation 

 that varies in extent in different genera. Each division is furnished 

 with fine strong ciliated spines, which stand on their own well-defined 

 lobes, and the outer angle is armed with a short sharp tooth. 



The eyes are large and ovate. The first pair of antennas resemble 

 those of the Brachyura, they are single jointed, and support several auditory 

 cilia, and two ciliated hairs, one apical, and the other (the longer) sub- 

 apical. The second pair of antennas consist of a basal joint and two appen- 

 dages: one is cylindrical, and tipped with two or three long ciliated hairs; 

 the other is formed into a broad flat squamose plate, straight on the outer 

 side, where it terminates in a strong tooth, and arched on the inner side, 

 and fringed with numerous long spinous hairs richly furnished with cilia. 



