316 BULLETIN OF THE 



The posterior border of the telson (PI. II. Fig. 15, t) now but slightly 

 exceeds the anterior end in width. It is deeply concave, and furnished 

 with but eight long setae. The spaces between the long seta) contain two 

 very small setae ; those in the median interspace are longer than the rest. 



It appears from my notes that on the 8th of August, 1878, a speci- 

 men in the stage described above as the third moulted in one of my 

 aquaria, and then appeared in a shape differing in one respect from that 

 which I have just described as the fourth larval stage. Besides the 

 acquirement of the sixth pair of swimming-feet, the seventh pair were 

 developed in this specimen as biramose, clearly segmented, setiferous 

 appendages (PI. II. Fig. 14), but very small in size compai-ed with the 

 sixth and preceding pairs. The last pair of thoracic limbs were simple, 

 sac-like organs. This early development of the seventh pair of swim- 

 ming-feet I regard as premature ; in the normal course of development 

 it is anticipated by the eighth pair, as will appear presently.* 



Fifth Larval Stage (PI. III. Figs. 4- 13). — This stage was reared from 

 the fourth stage in one of my jars. The most important structural ad- 

 vance upon the preceding stage consists in the full development of the 

 hindmost pair of thoracic appendages. The flagellum of the second pair 

 of antennae has increased in length, and the long tei'minal segment shows 

 a faint indication of division into four segments. There is a short spine 

 (Fig. 4, 77, sp.)' on the outer side of the distal end of the posterior 

 antennae, which becomes larger in later stages of the development. This 

 spine is more highly developed in the larvae of Paguridoe, and represents 

 the enormously developed spinous process of the second pair of antennae 

 so frequently found in the zoeae of the Brachyura. From the exuviae of 

 one individual I obtained for the first time the complete structure of the 

 mandible (Fig. 7, III). It is composed of two branches, as in the adult, 

 but the anterior branch, instead of presenting a molar crown, as in the 

 full-grown animal (PI. IV. Fig. 19), ends in multidenticulate incisor 

 edge. This branch is concealed beneath the fleshy Jabrum, and hence 

 escaped detection in the earlier stages. 



The chela of the fourth pair of swimming-feet is more perfectly formed 

 than before, the penultimate segment being much enlarged, with its 

 internal angle produced as far as the middle of the terminal segment 



* I find among some larvae which I preserved in alcohol one specimen with five 

 pairs of natatory appendages (in this agreeing with the third stage above described), 

 but in every other respect agreeing with the fourth stage. Behind the last pair of 

 swimming-feet are the double, sac-like rudiments of the two following pairs. Length, 

 4 mm. 



