COMPLEMENTAL MALE. 231 



Varieties. — The specimens from near Naples, (which I 

 owe to the kindness of the Rev. F. W. Hope,) are some- 

 what larger, and differ slightly from those of Britain : 

 they form, I imagine, the S. Sicilice of Chenu. After 

 carefully examining them internally and externally, I 

 think it is quite impossible to consider them specifically 

 distinct, for although in several specimens, the valves 

 were placed a little further apart from each other, — the 

 upper latera a little more elongated, — the carinal latera 

 rather narrower in their upper half, — the infra-median 

 latera rather more rounded, — and, lastly, in the scuta, 

 the tergal margin extended almost in the same line wdth 

 the lateral margin ; nevertheless in other specimens, I 

 could perceive no difference whatever. It is, however, 

 remarkable that in several full-grown Neapolitan speci- 

 mens there were no Complemental males, whereas I have 

 never seen a single full-grown British specimen without 

 such being present. In some specimens in the British 

 Museum, without any given locality, I have observed 

 considerable variation in the breadth of the carinal and 

 rostral latera. 



COMPLEMENTAL MALE. PI. V, figs. 9 14. 



When first dissecting Scalpellum vulgare, I was sur- 

 prised at the almost constant presence of one or more 

 very minute parasites, on the margins of both scuta, close 

 to the umbones : these are represented, but rendered 

 darker and therefore more conspicuous than in nature, 

 in the drawing, PL V, fig. 15, w T hich is three times the 

 natural size. I carelessly dissected one or two specimens, 

 and concluded that they belonged to some new class or 

 order amongst the Articulata ; but did not at that time 

 even conjecture, that they were Cirripedes. Many months 

 afterwards, when I had seen in Ibla, that an hermaphrodite 

 could have a complemental male, I remembered that I 

 had been surprised at the small size of the vesiculae 

 seminales in the hermaphrodite S. vulgar e, so that I 



