3(52 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



stage there are no traces of any abdominal appendages, but in the second stage, the outlines of 

 the sixth pair are faintly visible under the cuticle of the telson, as shown in PI. xvi, Fig. 2. 

 The stomach is almost completely free from yolk, and the surface of the body is marked by 

 red and yellow pigment spots, which are very constant in position and number, and are well shown 

 in the figures. 



As shown in PI. xvi, Fig. 2, the antennule consists of a stout shaft composed of a long basal 

 portion with no trace of an ear and a much shorter distal joint, which carries externally a much 

 shorter and smaller joint with four sensory hairs, and internally a long slender plumose hair, which 

 is not fully extended until after the first moult. At this stage this hair is almost sessile upon the 

 shaft, although its base is destined to give rise to the long flabellum of the antennule of the 

 adult. 



The antenna has a large exopodite, which is fringed with plumose hairs, and is an efiScient 

 organ of locomotion. During the first larval stage this e.xopodite, which is destined to become 

 the flat scale of the adult antenna, is cylindrical and distinctly annulated, as shown in PI. xvi, Fig- 

 4. At this stage it is divided into a basal portion and five movable joints, about equal in total 

 length to the basal i)ortion. After the first molt the annulations become less distinct, although 

 the "scale" is still cylindrical, as shown in PI. xvi. Fig. 2. The basal joint of the antenna is about 

 equal in length to the "scale," undivided, and it carries upon the inner edge of its -distal extremity 

 a small, short, movable joint, with a single, long, plumose hair, which is "telescoped" before the 

 first moult, but fully extended afterwards. This short joint is the rudimentary antennal fla- 

 gellum, which in the adult is equal in length to the entire body of the animal. 



The mandible is shown in Fig. 8. It is deeply cleft into two branches, the outer one with two 

 rows of large, strongly marked dentations, and the inner one with a rudimentary palpus, two rows 

 of hairs, and a finely serrated cutting edge. The first maxilla is very small, but it does not appear 

 to be rudimentary. It is shown in PI. xvi, Fig. 6. No exopodite could be made out. There is 

 a small endopodite, with one long, plumose hair, and two basal joints, one with two sharp cutting 

 hairs and the other with one. The second maxilla is shown in PI. xvi, Fig. 7. The two basal 

 joints are feebly indicated, and each carries three slender, simple hairs. The endopodite carries 

 two terminal hairs, and the flat exopodite is fringed by seven. I could not determine whether 

 these hairs are plumose or not. The three pairs of maxillipeds are functional and they present 

 features which are characteristic of the genus Alpheus (see PI. xvi, Fig. 2). Each has a large, 

 flattened, polygonal, basal joint, which carries upon its inner edge a few short, sharp teeth, and 

 upon its outer edge a long, flat exopodite, with plumose swimming hairs, and an endopodite 

 which presents several peculiar features. 



The endopodite of the first maxilliped is very short and two-jointed, that of the second is 

 somewh.at longer and five-jointed, while that of the third is very greatly elongated, without traces 

 of joints, and ending in a long, simple hair which, as shown in PI. xviii, Fig. 4, is telescoped before 

 the first moult, but immediately afterwards becomes lengthened, as shown in PI. xvi, Fig. 2, untd 

 it reaches forward beyond the tips of the antennules and antenuje. Following the maxillipeds are 

 three pairs of buds to represent the first, second, and fifth pairs of thoracic limbs. The first bud 

 consists of a single branch, which is shown by its subsequent history to be the exopodite. The 

 second has two branches, a short exopodite, and an extremely short endopodite, while the third 

 consists of a somewhat longer, but still rudimentary, shaft, which represents the endopodite of 

 the fifth tlioracKi limb, and has no trace of an exopodite. 



The hind body is divided by joints into five abdominal somites, behind which is a long undi- 

 vided region to represent the sixth abdominal somite and the telson. Before the first moult none 

 of the abdominal appendages are present, but after this molt the sixth pair are faintly indicated 

 under the integument of the telson, as shown in PI. xvi. Fig. 2. The telson itself is broad, sub- 

 triangular, with Its posterior border nearly straight and transver.se. It carries eight pairs of stout 

 plumose hairs, of which three pairs are much longer than any of the others and nearly equal. 

 This set of three spines is i)laced at the angle of the posterior edge on a lobe or elongation, which, 

 while it IS so slightly marked as to scarcely interrupt the triangular outline, is still very distinct 

 and easily recognizable. Of the remaining five spines on each side of the middle line, one is on 

 the external border, and the other four on the posterior edge between the group of three and the 

 middle line. The internal one is very small and might easilj- be overlooked. 



