262 SCALPELLUM ROSTRATUM, 



Caudal Appendages, spinose, uni-articulate ; but the 

 specimen was injured, and I could not exactly make out 

 their shape : I believe it was oval, and thickly fringed with 

 fine spines. 



Penis, very small, almost rudimentary, narrow, and 

 hairy, scarcely exceeding in length the pedicel of the sixth 

 cirrus. 



COMPLEMENTAL MALE. PI. VI, fig. 5. 



Before describing the parasite of the present species, 

 which departs entirely from the character of the males of 

 the three preceding species, it is proper to state that I 

 consider it to be a Complemental Male simply from 

 analogy, as will hereafter be more fully shown at the end 

 of the genus. Had a specimen of the parasite been 

 brought to me without any information, I should have 

 concluded that it was an immature individual of a new 

 genus of pedunculated Cirripedes, remarkable from the 

 rudimentary condition of the valves, and exhibiting, in 

 one important character, namely, in the form of the 

 larval prehensile antennae, an alliance to Scalpellum. 

 Had I been then told that three individuals in a group, 

 had been found attached to S. rostratum, not outside 

 the valves, but to the integument, in a central line, 

 between the labrum and the adductor scutorum muscle, 

 in such a position that when the Scalpellum closed its 

 valves, these parasites were enclosed within the capitulum, 

 my surprise would have been great ; for it is very im- 

 probable that this singular and unparalleled position 

 was accidental in this one group of specimens, inas- 

 much as there seems to be a relation between the naked 

 condition of the capitulum of the parasite, and the pro- 

 tection afforded to it by the capitulum of the Scalpellum. 

 It further becomes apparent on reflection, that these 

 minute parasites, though having the appearance of im- 

 maturity, can not increase in size, or but little, for if they 

 did grow, and acquired an ordinary size, they would 



