50 Dr. F. Miiller on the Transformations of the Porcellanae, 



Porcellana CrepUnii lived ; but the larvae of the common and of 

 the smaller PorcellancE are distinguishable at the first glance by 

 the posterior processes of the carapace ; and thus this larva may 

 without hesitation be referred to the former species, from the 

 earliest form of which it differs only by having twelve (instead 

 of ten) setae on the caudal segment, and by the presence of a 

 pair of short inarticulate appendages on each of the four pre- 

 ceding segments. This single larva was, fortunately, uncom- 

 monly instructive, inasmuch as, being near its change of skin, 

 it already showed the new limbs, with variable distinctness, 

 within the old ones. 



The new external antennae had a multiarticulate flagellum ; 

 feet with large chelae ; and other members, which could not be 

 completely made out, were situated behind the natatory feet ; 

 and within the caudal segment was a fan-shaped fin (fig. 7). 



Hence, although the larva itself approaches closely to the 

 earliest stage, the animal issuing from the next change of skin 

 could scarcely diffier essentially from the mature Porcellana. 



So far my observations adapted for a preliminary communi- 

 cation. Their results may be summed up in a few short pro- 

 positions : — 



The Zoea-iovxa of the Crabs is completely destitute of the five 

 pairs of true feet, and even of the segments bearing these. 



The natatory feet of the Zo'ea become the foot-jaws of the 

 Crab. 



The Porcellance are Crabs which have remained stationary at 

 the Meffalops-stage'^. 



EXPLANATION OF PLATE L 



Fiff. 1. Porcellina stellicola, n. g. and sp. ; magnified 5 diameters. 



Fig. 2. Its external antenna; magn. 25 diam. 



Fig. 3. Fifth pair of feet of the male; magn. 45 diam. 



FHg. 4. Its youngest Zoea-forra, from above; magn. 15 diam. 



Fig. 5. Cephalic portion of the preceding, from below ; magn. 90 diam. : 



a, anterior, and b, posterior antennae ; c, upper lip ; d, mandible; 



e, lower lip ; /, first, and g, second pair of maxillae. 

 Fig. 6. Older Zoea-form of the common Porcellana of Santa Catharina ; 



magn. 6 diam. 

 Fig. 7. Caudal extremity of the preceding; magn. 45 diam. In its in- 

 terior is seen the fan-like caudal fin of the next state. 

 Figs. 8 & 9. First and second maxillae of the youngest Zoea-form of the 



common Porcellana. 

 Fig. 10. Posterior process of the carapace of the youngest Zoea-form of a 



smaller Porcellana. 

 Fig. 11. External antenna of the youngest Zoea-form of a small Xantho : 



g, flagellum. 



* Milne-Edwards even places Megalops and Porcellana in the same 

 family. 



