258 SCALPELLUM RUTILUM. 



of these valves ; and from all the characters of the mouth, 

 S. rutilum is much more closely allied to JS. ornatum than 

 to any other species. 



MALE, OR COMPLEMENTAL MALE. 



In the concavity or hollow above the depression for the 

 adductor muscle (PL VI, fig. 2a), I found males, but in 

 so extremely decayed a condition, that they could hardly 

 be examined. On one side, however, I distinctly saw the 

 larval prehensile antennae, with pointed, hoof-like discs ; 

 and part of the thorax, with its small limbs and long 

 spines, as in S. vulgare or S. ornatum. I also saw clearly 

 the eye. The four calcified beads or rudimentary valves, 

 I believe, were present ; but in removing the specimen, 

 the whole fell to pieces and was lost. The outer integu- 

 ment was covered with rather thick, very minute bristles, 

 each about Tojooth of an inch in length, and therefore only 

 half the length of those on the complemental males of 

 S. vulgare. The cavities for the males are not formed, 

 as in S. ornatum, by the thickening of the internal surface 

 of the valve round a defined space, but by the scutum 

 being externally convex and internally concave down the 

 middle, hollows being thus produced both for the lodg- 

 ment of the males and for the attachment of the adductor 

 muscle. These hollows are separated from each other by 

 a slight transverse ridge. I do not know at which point 

 of the margin of the valve, the orifice of the male is situated, 

 but I presume close under the apex. In this species, as 

 in S. ornatum, there can be no question that the scuta of 

 the female are specially modified by their own growth for 

 the reception of the males. It must be added that, as it 

 was not possible to ascertain whether the ordinary form 

 of S. rutilum was hermaphrodite or female, so it must 

 remain doubtful whether the parasites are males or 

 complemental males; but the former, I think, is most 

 probable. 



