T. H. Withers — A new Girripede from Chalk Marl. 497 



adductor muscle pit, a slight ridge extends obliquelj- upwards and 

 inwards to the occludent edge, and above this ridge an obtusely- 

 angular portion of the valve is depressed and marked with growth- 

 lines, and evidently served for the reception of the scutal angle of 

 the tergura. 



Remarks and Comparison tvith other Species. — Although the four 

 carinse of S. parmdum are very small, the fact that they are all of 

 about the same size seems to show that they are mature valves. 

 A large amount of material has been carefully looked over, but these 

 four carinse only were found, so the species is probably rare. 



The known Cretaceous species with the umbo of the carina situated 

 sub-centrally number three only, namely, 8. heisseli, Bosquet and 

 Miiller,^ S. danviniantiyn, Bosquet,* and S. hagenovianum, Bosquet,^ 

 one of which 8. darwinianum, has been described ^ from the Upper 

 Senonian of Salisbury, Wilts. 8. parvulum is (^uite distinct from 

 8. beisseli and 8. darwituaniim, for in these two species the upward 

 growth of the carina is due to the almost equal upward and 

 downward growth of the valve from the umbo, the parietes and 

 intraparietes are not defined, and the outer surface is ornamented 

 vrith numerous ridges radiating from the umbo. 8. hagenovianum 

 agrees in the upper part of the valve being formed by the upward 

 growth of the intraparietes beyond the umbo, but difPers among other 

 characters in the intraparietes being ornamented with ridges, and in 

 the tectum being flatly arched transversely with a rounded ridge on 

 either side. The carina of 8. parvulum resembles more closely that 

 of the Tertiary 8. magnum, Darwin, but in the absence of the 

 remaining valves of the capitulum it is impossible to say whether the 

 two species are related. In 8. magnum the inner margin of the carina 

 is markedly concave, and on the inner side the valve is usually 

 narrowed below the umbo, whereas in all the carinse of 8. parvulum 

 the inner margin is straight and the valve is not narrowed below 

 the umbo, but widens gradually downwards from the apex and is 

 expanded near the base. Moreover, in 8. magnum the tectum is 

 separated from the parietes by a ridge, while in 8. jmrrtdum the 

 tectum and parietes are not defined. Although the absence of 

 a ridge between the tectum and parietes may seem a trivial point, 

 this ridge is clearly seen in quite young valves of 8. niagtmm. 



As regards the scutum tentatively considered as belonging to 

 8. parvulum, it has the umbo at the apex, and therefore differs from 

 8. magnum, 8. beisseli, and 8. darwinianum, which all have the umbo 

 situated sub-centrally ; in its other characters it differs markedly 

 from these and other known species. The scutum of 8. hage^ioviamim 

 is not known. 



^ J. Bosquet, Notice sur quelques Cirripides ricemment ddcouverts dans le 

 Terrain Gritaci du Duch4 de Limbourg, Haarlem, 1857, p. 7, pi. i, figs. 4-7. 



- J. Bosquet, Monogr. Crust. Foss. du Terr. Cret. du Duche du Limbourg, 

 1854, p. 46, pi. iii, figs. 6-12. 



' Tom. cit., p. 49, pi. iv. figs. 13-16. 



^ T. H. Withers, " Some Cirripedes from the Chalk of Salisbury, Wilts" : 

 Geol. Mag., Dec. V, Vol. VIII, p. 23, Figs. 3-4. 



DECADE VI. — VOL. I. — NO. XI. 32 



