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Preliminary remarks. I owe to the kindness of Professor Steenstrup, as in so many former instances, an examination of several specimens of this fossil, which is of interest, as being extremely common and characteristic of the white chalk of Denmark. Among the numerous minute specimens from the chalk detritus of Charing in Kent, sent me by Mr Harris, there are some carinae so similar that I have ventured, with doubt, to rank this as a British species; the carina, however, in this species, are far from characteristic. I have felt much hesitation in admitting this species in the genus Scalpellum: Professor Steenstrup was originally inclined to believe that the capitulum was formed of only five valves; could this be proved, the species would very naturally rank with a small recent one from the Island of Madeira, which, owing to the upward growth of the scuta, and to certain peculiarities in the animal’s body, I have felt myself compelled to raise to the rank of a genus, under the name o f Oxynaspis. But as the valves of S. (?) cretae have never been found united, and as the main ones are very small, fragile, and generally in a broken condition, the small lower ones might easily be overlooked. I have seen, indeed, in two instances, /

[4 6 ] W O R K S OF d a r w i n : v o l u m e 1 4 what appeared to be upper latera, but as I could not remove them so as to examine their undersides, I am far from sure that they were not broken, angular portions of scuta. I f we look to the character o f the separate valves, there is a striking and important resemblance between the scuta of S. cretae and tuberculatum, in the umbo being seated in a nearly middle point o f the occludent margin, and likewise in the two ridges running from the umbo to the baso-lateral angle, and to a central point of the basal margin; in which latter character of the ridges, this species also agrees with S. semiporcatum. These facts have determined me, provisionally, to rank the present species under Scalpellum. But on the other hand, if we look to the carina, which, according to our rule, is considered the characteristic valve in this genus, it rather resembles the homologous valve in Pollicipes; for the carina has not any parietes separated from the tectum by a distinct ridge. The terga seldom afford any serviceable generic characters; but as far as they go, they also rather resemble the terga in Pollicipes than in Scalpellum. Hence, it is obvious, that the generic position of S. (?) cretae is at present very uncertain.