320 BULLETIN OF THE 



almost every detail like that of the adult prawn, parts of which are 

 represented on Plate IV. Figs. 16-31. The integument, however, is 

 much thinner and more transparent, the legs are longer, and the exter- 

 nal plate of the swimmerets is not divided by a transverse suture. The 

 rostrum (PI. IV. Fig. 32) is nearly as long as the portion of the carapace 

 behind it. Viewed in profile, it increases in depth from the root to 

 beyond the middle, thence tapers with a gentle upward curve to a fine 

 point at the tip. It is armed above with seven, below with three, teeth. 

 The second tooth, counting from the base, lies over the proximal end of 

 the eye-stalks. They are all directed forward, and in the intervals be- 

 tween them are two or three hairs. 



As the prawn develops, new teeth are added between the older ones 

 and the tip of the rostrum. In a specimen which measures 9 mm. 

 in length, the dental formula is | (PI. IV. Fig. 33). In the mature 

 prawn the number of teeth on the rostrum is commonly nine above and 

 four below (PI. IV. Fig. 30), but is subject to great variation. Thus, I 

 find on looking over a large series of specimens measuring from 28 mm. 

 to 42 mm. in length, the following formulae for the rostral teeth : 



■V-, ¥, ¥> I. h I. I. I, I, h I, §■ 



Hence will appear the folly of those zoologists who have taken the form 

 of the rostrum as a means for distinguishing species in the group of 

 Caridea. The carapace is provided, moreover, with an antennal and a 

 branchiostegal spine on the fore margin of each side. There is now no 

 trace left of the large supra-orbital spine which was so conspicuous in 

 most of the larval stages. The pterygostomian angle is rounded off as 

 in the full-grown individuals. The pleurae of the fifth abdominal seg- 

 ment extend backward over the following somite, but are not drawn out 

 into a long spine as in the larval stages. 



The telson has the same form and armature as in full-grown speci- 

 mens. It tapers posteriorly to a very narrow hind margin which is pro- 

 duced in the middle in the form of a stout tooth. From the lower face 

 of this median tooth issue a pair of long, plumose setae. On each side 

 of the median tooth is a long spine, which is articulated with the telson, 

 and outside of these is a short spine, similarly articulated with the 

 external angle of the posterior border of the telson. The dorsal surface 

 of the telson has four small spines arranged as in the mature prawn. 



The third flagellum of the first pair of antennae is now present as a 

 short, two-jointed appendage tipped by fine hairs (PL IV. Fig. 15, re'). 

 It does not issue from the peduncle of the antennule, but from the inner 



