MUSEUM OF COMPARATIVE ZOOLOGY. 257 



On several warm, still mornings in August, 1878, the zoese of Porcellana 

 swarmed in the streaks of smooth water on the edge of the tidal currents at the 

 mouth of Narragansett Bay.* They are sluggish, and move either forward or 

 backward. The little spines with which their enormously developed rostra are 

 armed serve to accumulate the minute particles floating in the water to such 

 an extent that the little creatures often become quite conspicuous by virtue of 

 the load of dirt which they carry. 



Of the numerous specimens which I collected almost all were in the stage 

 immediately preceding the youngest stage of the crab, into which they readily 

 developed in confinement, and some of which were taken from the sea with the 

 zoese. 



Specimens in the last zoea-stage (PI. II. Fig. 1) measure about 16 mm. from 

 the tip of the rostrum to the tips of the posterior spines of the carapace. The 

 rostrum is 11 mm. long, the posterior spines 2.5 mm. 



Viewed from the side, the carapace is of a long oval form, extending forward 

 as an enormous rostrum, and backward into two horns curved slightly down- 

 ward at their ends. The rostrum is furnished with five rows of little spines 

 disposed as shown in the cross-section (PI. II. Fig. 3). The posterior horns 

 have a single row of spines below (PL II. Figs. 2, 4). The first pair of an- 

 tennas (PL II. Fig. 6) are composed of a long peduncle which is obscurely 

 divided into two or three segments. At its base there is a slight enlargement 

 which contains the auditory apparatus (a). The peduncle bears a blunt process 

 (b), and a longer segment (c) which is furnished with several sensory threads 

 (d). The second pair of antennae consist of a two-jointed peduncle, in the 

 basal segment of which may be seen the orifice of the renal organ (c). Of the 

 two branches borne by the peduncle, the inner (a) is the longer, and within 

 its transparent integument is seen the multi-articulate flagellum of the antenna 

 of the crab, to be disclosed at the next moult. The outer branch (b) is styli- 

 form. The mandibles have a many-toothed crown (PL II. Fig. 8), and the 

 palpus is represented by a very small protuberance (a).t The bilobed metas- 

 toma is armed with short setae on the inner margin of each lobe (PL II. Fig. 

 9). The first pair of maxillae consist of an inner lobe (PL II. Fig. 10 a) and 



* I am indebted to Mr. Agassiz for the facilities for investigation afforded by his 

 laboratory at Newport, R. I. 



t Although this is certainly the last stage of the zo'e'a (I obtained the young crab 

 from it after a single cast of the skin), the mandibular palpus is not developed to 

 anything like the extent seen in Dohrn's figure of a Porcellana zoea. (Untersu- 

 chungen iiber Bau und Entwicklung der Arthropoden. Zeits. Wiss. Zool. XXI. 

 p. 373 ; Taf. XXIX. Fig. 51. 1871.) Claus, describing a Porcellana zoea from 

 Nice in a stage corresponding to the one before us (Marburger Sitzungsberichte, 

 1867, p. 15), states that the mandibles are destitute of palpi ; but in his later work, 

 " Untersuchungen zur Erforschung der Genealogischen Grundlage des Crustaceen- 

 Systems," 1876 (p. 58), describing the same stage, he says the rudiment of the palpus 

 exists as a simple prominence. 



