378 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The antennules consist of a stoat jointed stalk, the terminal segment of which bears four 

 sensory filaments.\ A long plumose spine springs from the extremity of the second joint on the 

 inner side. 



Tlie antennte are biramous, the two branches arising apparently out of a common basal segment. 

 The outer division is a scale-like plate. It bears on its extreme inner border a row of i)lumose hairs, 

 eight to ten in number. The endopodite is slender and shorter than the scale. It terminates in a ■ 

 short spine or defaticle, from near the base of which springs a long plumose hair. The eyes are 

 large and uncovered. The mandible is simple. 



The telson is a broad triangular plate, the terminal side of which is garnished with the charac- 

 teristic zocal spines, the number, relative size, and position of which vary slightly in the different 

 species. There are in this case eight pairs of these spinfes. The first or median pair is rudimen- 

 tary; the secoud is not half the length of the third. The lateral angles of the plate are each 

 prolonged into a short lobe, bearing three spines. There is no marked median notch, but there is 

 a slight median depression. The rudiments of the sixth pair of abdominal ajipendages are plainly 

 seen. 



Second larva. — With the first molt the endopodites of the maxillipeds lengthen. Three pairs 

 of rudimentary pereiopods are now present, the last of which are the longest. Of the pleopods 

 only the sixth pair are represented, whether free or not was not observed. 



ALFBEUS HETEROCHELIS FROM BEAUFORT. 



The peculiar metamorphosis of the Beaufort Heterochelis was described in 1884 by Brooks, who 

 also showed that in this respect it departs widely from the associated Alpheua mmus. 



The form in question is hatched as a larva with preparations for the schizopod stage. It has the 

 usual swimming organs, but all the thoracic legs are present in the condition of rudimentary buds. 

 Tiie abdominal segments are formed, and the buds of the first five paiis of feet belonging to them. 

 The eyes are not completely covered by the carapace. At the first molt the rudiments of the 

 sixth pair of abdominal feet are added, and the larva undergoes profound changes. All the ap- 

 pendages are now functional and the eyes are nearly hooded. With later molts the adult char- 

 acters become more pronounced, but the marked difference of the great claws appears only after 

 several months. 



ALPHEUS HETEROCHELIS FROM FLORIDA. 



The short description, given by Packard in 1881, of the first larval stage of this species from 

 Key West, where it inhabits sponges, has already been alluded to. From this we infer that the 

 development is considerably more abridged than in the Beaufort case. This is also indicated by his 

 figure of one of the abdominal appendages. He says : The eyes are nearly sessile, the yolk nearly 

 absorbed, although the embryo (in the egg) was near the time of liatching. The antennse are " well 

 developed." All the thoracic legs are present, their joints distinct, " the first pair about twice 

 as thick as the others, the claws rather large, but not so disproportionately so as in the adult form, 

 but as much so as in the larva in the second stage of the lobster. Abdomen broad and fiat, spatu- 

 late at the end, much as in the adult. There were five pairs of abdominal feet or swimmerets, each 

 with endopodite and exopodite, like those of the second larval stage of the lobster." 



ALPHEUS SAULCYI FROM THE BAHAMAS. 



In this form, the metamorphosis of which is fully described in another paper, we have either 

 an abridged development in which the general adult ch.aracters, very marked in the first larva, 

 are all acquired in twenty four lionrs after hatching, or a case where the short metamorphosis is 

 done away with entirely, so that the animal leaves the egg in the full adult form. 



Comparing the histories just given with the one before us, we find that the first larva of 

 AlphcHs sauleyi is about equivalent to the third larva of the Heterochelis from Beaufort, and rather 

 more advanced than the first larva of this species from Florida. 



Tlie eggs of the Alphei, with the development unabridged, are invariably small and quite 

 numerous. In the two species, however, with .shortened metamorphosis, the ova are fewer and many 

 times larger. Moreover, as would be expected, the degree of abbreviation is correlated with the 



