No. 15. — On the Development of Pal^monetes vulgakis. 

 By Walter Faxon. 



The observations recorded in this paper were made during the sum- 

 mers of 1876 and 1877 in the laboratories of Mr. Alexander Agassiz, at 

 Newport, E. L, and of the United States Commission of Fish and 

 Fisheries, at Wood's Hole, Mass. I am under great obligations to Mr. 

 Agassiz, and Professor S. F. Baird, United States Commissioner of Fish 

 and Fisheries, for placing at my disposal every means for the collection 

 and study of specimens. 



The difficulty of rearing the larva; of Crustacea in confinement, and 

 the uncertainty of finding all the stages in the development of a species 

 by collecting with the hand-net or tow-net, perhaps account for the 

 fact that we have so few life-histories of Decapod Crustacea which are 

 in any way complete. 



The common prawn of our coast, Pakemonetes vulgaris Stimpson, is 

 one of the most typical of the long-tailed Decapods, and affords an 

 excellent opportunity for obtaining the life-history of a Macrouran, 

 which undergoes a metamoi'phosis after quitting the egg. The present 

 paper is a contribution to that history. 



The opacity of the eggs and larva? making it impossible to follow the 

 development of the internal organs in detail, I have confined myself 

 chiefly to the growth of the hard parts. 



This species was first described by Say, in 1818, under the name of 

 Pal&mon vulgaris ; * again described, and figured for the first time, by 

 De Kay, in 1844. t In 1869, the genus Pakemonetes was established 

 by Heller for the reception of Palcemon varians Leach, from the North 

 Sea and fresh waters of the Mediterranean basin. % It differs from 

 Palcemon in lacking mandibular palpi. In the armature of the carapace 

 it agrees with Palwmon, subgen. Leander, i. e. an antennal and a 

 branchiostegal spine are present, but no hepatic spine. 



* An Account of the Crustacea of the United States. Jour. Acad. Nat. Sci. Phila., 

 Vol. I. pp. 248, 249. 1818. 



t Zoology of New York, Part VI. Crustacea, pp. 29, 30, PI. IX. Fig. 30. 1844. 



J Zur naheren Kenntniss der in den siissen Gewassern des siidlichen Europa 

 vorkommenden Meerescrustaceen. Zeitschr. wissensch. Zool., Vol. XIX. p. 160. 

 1869. 



