348 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



This larva is colorless, excepting large spots of reddish pigment, distributed much as iu the 

 previous stage. There is a spot near the extremity of the eye-stalk and similar ones on the abdo- 

 ineu. Some of the appendages are also tipped with brownish red. The attainment of the adult 

 characters is now mainly a question of the further growth of parts already present. 



The above outline gives us a pretty complete history of the metamorphosis of Stenopus. 

 Between stages B and C a lacuna occurs, but it is not difficult to bridge over this gap. The 

 development of Stenopus is especially interesting, inasmuch as it combines certain features of the 

 metamorphosis of Pena-us, Sergestes, Lucifer, and the Prawns in general, but it differs essentially 

 from any of them. Detailed comparisons are purposely omitted in this paper, but we will cull 

 attention to the apparent similarity of tbe second larva of Steuopus (PI. vni, Fig. 17) to the zoea 

 of Callianasxn xubterranm, figured by Glaus.* The length in each case is 5"" u . He says, p. 54: 



Die jnngen Calliauassa hirvm besitzen beira Verlassen der Eibiillcn oinc ausehuliche Griisse, sind sehr laug- 

 gestreckt und tragen droi spaltiistigo Fiisspaare, von denen eich das Voi-dern scbou wescntlioh der Formgestaltung 

 des spateren Maxillarfiisses niihert. Der lange Stirnschnabd, sowir dio Bestachelung don Abdomens, dessen zweites 

 Segment mit oinem besondera langen Riickendorn bewatl'ni't 1st errinern an die oben beschriebene larve. 



which applies perfectly to the Steuopus zoea, except that the latter has the first thoracic segment 

 with its appendages, while, according to Clans, the first zoea of Callianassa has not, although his 

 figure is not clear on this point. The rostrum, eyes, antenna;, second maxillie, and maxillipeds 

 are nearly identical in the two forms. The differences are in the shape of the telson and in the 

 condition of the thoracic appendages. The tail tin has a convex posterior edge, a median and two 

 lateral, short spines, and eleven intermediate pairs. The rudiments of the sixth pair of abdomi- 

 nal appendages show through the integument. Behind the maxillipeds, already "die kurzen, 

 schlauchformigen Anlageu samm timber Thoracalfiisse nnter dem Integument bemiirkbar sind." 



Among Ihe Prawns, Peureus has apparently preserved most completely the ancestral history 

 of the Decapod Crustacea, and for this reason a thorough knowledge of the development of related 

 species is very desirable. 



IV. THE ADULT. 



STENOPUS (Latreille). 



Cancer (Herbst). 



Palcemon (Olivier). 



Stenopus (Latreille) Le'ach, Desmarest, Eoux, Milne, Edwards, Adams, Dana, etc. 



Diagnosis of Stenopus h/spidus (Latreille). Body nearly cylindrical. Carapace with prominent rostrum and 

 distinct transverse groove. Outer antennae with long, bristle-bordered scale bent under the inner antennas 

 toward the middle line. Second maxillipeds with epipodite and long exopodite. Third maxillipeds very 

 long and appendicular, with a rudimentary exopodite at base. First, second, and third pairs of pereiopods 

 chelate. The first and second pairs quite slender, ending in small shears. Third pair longest, bearing the 

 large claws. Fourth and fifth pairs of pereiopods slender and uouchelate. Carpus and propodus of the same 

 articulated into numerous rings. First pair of pleopods uniramous in both sexes, all the others biramous. 



Special description. Length, 37-44 mm (li-lf inches). There is little difference in size between 

 the sexes, but the females are usually a trifle the larger. 



Color: Body invariably white, crossed by three bands of reddish crimson. Appendages col- 

 orless, excepting the third pair of pereiopods, which are encircled by four wide zones of the same 

 color. These markings are not of uniform tint, but vary from bright scarlet to mottled orange red. 

 The basal joints of at least the third and fourth pairs of thoracic legs sky blue. Antenna? snow 

 white. For further particulars under this heading, see PI. v, and Sec. i. 



The carapace (Fig. 37) presents a marked transverse fossa. It is covered with short dentiform 

 spines, largest on the front. The rostrum- is elevated, extending hardly beyond the basil joint of 

 the inner antenna?. It ends iu a sharp terminal spine and carries six to seven stout, curved teeth 

 on the dorsal median line, besides a single spinule projecting downwards near the tip. From the 

 single dorsal row of teeth two similar rows diverge, extending back to the transverse furrow. The 



*C. Clans : " Untersuchungen zur Erforschung der geuealogischen Grundlage des Crustaceen-Systems." Wien, 

 1^711. Taf. vni, Fig. 1 ; also Figs. 2-7. 



