//. Woodward — New Fossil Crustacea. 259 



of the circnmference of the conical walls of the shell ; the opercular 

 valves and base being absent. It would be impossible to speak 

 positively of such a fragment, were it not for the steeply conical 

 fonn and the rounded approximate, radiating ribs, which mark the 

 surface (PI. XIV. Fig. 2a). Viewed from above the costse are more 

 rounded and less prominent than in the Pyrgoma angliciim (Plate 

 XIV. Fig. 3), from which it also differs in its larger size and the 

 greater thickness of the shell-walls, and the obliquity of the cone. 



Diameter at base, 4^ lines; at apex, IJ line; height of shell, 5 

 lines. 



The ribs are crossed, at regular intervals, by well-marked lines of 

 growth, forming, with the costa3, a reticulated ornamentation on the 

 surface of the shell-wall, there being seven rings of growth in the 

 space of a line. 



The shell, if perfect, would probably have displayed about twenty- 

 five or thirty vertical costas, and about thii*ty-five transverse rings. 

 The interior of the shell is smooth, and the wall is nearly one line 

 in thickness near its base. No sutures are visible, the parietes 

 having, apparently, all coalesced in the adult, as is the case with the 

 recent species of Pyrgoma. 



M. Bosquet, of Maestricht, has already figured and described a 

 species of Verrm^a from the Uppermost Chalk.^ 



Dr. Darwin has also shown that the species common to our Eed 

 and Coralline Crag, and to the Glacial deposits of Scotland, is 

 identical with the living Verruca stromia of our British seas (Mon. 

 Foss. Cirripedia, p. 42, T. 2, f. 9). 



We have now another sessile cirripede, embracing the same range 

 in time — in the case of Pyrgoma, not parasitic upon shells (like 

 Verruca), but fixed to the cup of a coral ; and it is interesting to find 

 it associated with the same form of corals, both in the Chalk and in 

 recent seas ; serving as an excellent illustration of the principle, so 

 universal in Natural History, that whenever conditions are the same, 

 similar associations of animals recur, even through periods of time, 

 far beyond our powers to estimate. 



II. ' Necrocarcinus tricarinatus, Bell. — In Professor Bell's Mono- 

 graph on the Crustacea of the Gault and Greensand (l^al^eonto- 

 graphical Soc. Mon. 1862, p. 19,) he adopts the name Necrocarcinus 

 for certain forms of Crustacea, from the Chalk-marl and Upper 

 Greensand, figured and described by him, and referred (not, how- 

 ever, without some doubt) to the family of Corystidce. To this 

 genus I wish now to call attention, and especially to the species 

 N. tricarinatus (ib. p. 21). The examples figured by Professor Bell 

 are from the Upper Greensand of Cambridge and of Wiltshire. 

 "The margin of tlie specimen described," writes the author, "is 

 much broken, so that we are left to speculate in some measure 

 upon the exact figure of the carapace ; but, following the line in- 

 dicated by the portions which remain entire, it appears to be less 

 uniformly rounded than in Necrocarcinus Woodwardii. 



1 Verhandelingen Geologische Beschrijving en Kaart van Nederland. Haarlem, 

 - " -16. 



