OF THE PUKBECK FOKMATION. 331 



Tube 61. Cythere retirugata and its var. rugulata, ordinary ; and 

 one Cypris purhecJcensis : 20 specimens altogether. In both 

 60 and 61 rugulata is more common than the other. 



Tube 62. Cypridea punctata ; very large. jS"umerous ; about 80. 



Tube ^2*. Candona hononiensis and C. ansata (both ordinary), 15 ; 

 and Cypridea punctata (ordinary), only one. 



Tube 65. Cypridea punctata^ ordinary ; and C. Dunkeri^ like that 

 of tube 59, more numerous than C. punctata ; about 250 of 

 the two together. 



Certain strata at Swindon containing '^ Cyprid.es " are described, 

 loc. cit., as freshwater marls and limestones, 10 feet thick, with depres- 

 sions (" pipe-like veins ") in them, containing material derived from 

 the Lower Greensand. Further, they are referred to as chalky 

 limestones, in which are one or two darkish bands of earthy, car- 

 bonaceous marls and loose grits, containing mixed marine and fresh- 

 water forms. C. Moore also remarked that " the chalky limestones 

 or marls contain few remains of recognizable character "; but, to- 

 gether with several smaller derived fossils, he got four or five species 

 of Cypris " from the black bands," or " earthy carbonaceous marls 

 and loose grits " (the '^ black carbonaceous friable loam,'' Hudleston, 

 op. cit. p. 548). The specimens in the tubes above referred to are 

 (from both internal and collateral evidence) believed to be Mr. C. 

 Moore's Swindon specimens. 



These deposits t were referred to the Middle Purbeck, with some 

 doubt, by Mr. C. Moore ; and he suggested that Purbeck beds of 

 older date may have been cut into, disturbed, and mixed up with 

 them. Prof. Morris gave his opinion (p. 547) that these beds 

 " might be the equivalents of the entire thickness " of the Purbeck 

 series (300 feet at Durlston Eay). 



Either of these suggestions will account for the occurrence of the 

 Lower-Purbeck species : — retirugata., rugidata, hono7iiensis, ansata. 

 and purhechensis in company with DunTceri and punctata. Had 

 fasciculata turned up also, we should have had a fairly representative 

 and complete group. 



§ Y. Conclusion. 



In conclusion there are fourteen species of Ostracoda in E. Eorbes's 

 three divisions of the Purbeck series of deposits. Five of them 

 occur only in the Lower Purbeck. Of the others, six occur in both 

 the Middle and the Upper. Of the fourteen, five go up into the 

 Wealden, from the Middle and Upper divisions only. See the fol- 

 lowing Table (p. 332). Cypridea punctata for the Upper, C. granulosa 

 ( fascicidata) for the Middle, and Cypris purheckensis for the Lower 

 Purbeck, are especially characteristic. 



t At p. 548, op. cit., Mr. Hudleston notes that this " black carbonaceous 

 friable loam " becomes further on a bed of Cerithium portlandicum in " dark 

 friable marly grit," and " that above this bed the regular Portland Limestone 

 comes on again," " Purbeck " and " Portland " conditions inosculating at this 

 spot. Prof. Blake's interpretation of the section is different. 



