SCALPELLUM. 15 



here repeat the remarks made iu the Introduction on the great difficulties in classifying the 

 recent species, and still more the fossil species of Scalpellum. I may, however, here state 

 that should the S. vulgare be hereafter kept distinct in a genus to itself, S. magnum would 

 have to go with it. Should a recent species, which in a future work I shall describe under 

 the name of 8. rutilum, be generically separated, it will probably have to bear the name of 

 Xiphidium, from its alliance to the Eocene X. qiiadraium of Sowerby, to which species the 

 cretaceous 8. fossida and several other forms are apparently closely allied. These latter 

 species, however, are likewise closely allied to the Scaljoellujii ornatum, which Mr. Gray has 

 already raised to the rank of a genus under the name of Thaliella. There are some 

 fossil species, as 8. arcuatum, and simplex and solidulum, which I cannot rank particularly 

 near any recent forms. Mr. Sowerby founded the genus Xiphidium on the umbo in the 

 Carina being situated at the apex, and on its growth being consequently exclusively 

 downwards. This is likewise the case wdth the recent 8. rutilum ; but I shall have 

 occasion to show, under 8. magnum., that the upward growth of the Carina in that 

 and other species of the genus, depends merely on the intra-parietes, which are present in 

 many species, meeting each other and being thus produced upwards. Moreover, in the 

 recent 8. ornatum, the position of the umbo is variable, according to the age of the 

 specimen ; in half-grown individuals being seated at the apex, and in large specimens 

 being sub-central, as in 8. vulgare, magnum, and other species. I should have been very 

 glad to have retained the genus Xiphidium, but taking into consideration the whole 

 organisation of the six recent species, I can only repeat that we must either make six 

 genera of them, or leave them altogether, and this latter has appeared to me the most 

 advisable course. 



8exual Peculiarities. — For reasons stated in the Introduction, I have kept the genera 

 Scalpellum and Pollicipes distinct ; but I may mention, in order to call attention to a point 

 of structure which may hereafter be discovered in some fossil species, that I was much influ- 

 enced in this decision by some truly extraordinary sexual peculiarities in all six recent species 

 of Scalpellum. 8calpellum ornatum is bisexual ; the individual forming the ordinary shell, 

 is female ; each female has two males (a case oi Diandria motioggnia), ^vhicli are lodged in small 

 transverse depressions, one on each side, hollowed out, on the inner sides of the Scuta, close 

 above the slight depressions for the adductor scutorum muscle ; in 8. rutilum ^^ 



(nov. spec.) two males are lodged in the same place on each side, but rn^^m^' 

 rather in concavities in the valve, than in distinct depressions. As these are j^ WwM'^^^ 

 the two recent species most nearly related to several Cretaceous and Eocene fiW^^^ 

 forms, we might expect to find similar depressions in some fossil species ; but )M!l^^^ 

 as yet I have not succeeded in distinctly finding such. The male cii-ripedes lli^^^^^l 

 are very singular bodies ; they are minute, of the same size as the full- "^^^^^^^ 

 grown larva : they are sack-formed, with four bead-like ruchmental valves at inside vie^r of the scutnm 



o d m Sc/itpe(lufn ornatum^ 



their upper ends ; they have a conspicuous internal eye ; they are absolutely the iaductotmusd"" ^"' 

 destitute of a mouth, or stomach, or anus : the cirri are rudimental and furnished 



