108 HALKYARD, Fossil For aminif era of the Blue Marl 



The above is the generic description given by Schlum- 

 berger in "Note sur les genres Trillina et Linderina" (Bull. 

 Soc. Geol. de France, 3e serie, tome XXI (1893), p. 120), 

 and requires some modification to include such members of the 

 genus as the two new ones described below which undoubt- 

 edly must be classed in the same genus. The only species 

 described by Schlumberger (L. brugesii) differs slightly 

 from his generic description inasmuch as the chambers are not 

 all in the same horizontal plane, the disc of chambers being 

 slightly hollowed on the inferior surface, if one disregards the 

 prolongations of the chamber-wall which cover the previously 

 formed rows of cells and cause the thickening of the central 

 portion of the disc. This hollowing of the inferior surface, 

 which is noted by Schlumberger in his description of 

 L. brugesii, is carried to such an extent in my 

 L. chapmani as to produce a test similar in 

 appearance to Patellina, or some forms of Cymbalo- 

 pora with which latter genus Linderina is closely allied, the 

 shell-wall in both genera being of the same character, and both 

 forms having a small spiral commencement to the test followed 

 by concentric rows of chambers, the cells of each row alter- 

 nating with those of the previous row, so that the centre of each 

 chamber is opposite the point of junction of two chambers of 

 the preceding ring, after the manner of Planorbulina and 

 Cymbalopora. 



In my opinion, after careful study of specimens of L. ovata 

 mounted in Canada Balsam, Schlumberger is mistaken in 

 affirming that "the wall of all the chambers is continuous on 

 all the circumference, without any trace of suture, and is cor- 

 rugated in order to form each of the little chambers." I have 

 observed this apparent duplication and corrugation of rhe cell 

 wall which can only be seen in very few cells of the many com- 

 posing a single test, and am satisfied that it can be accounted 

 for in other ways such as cutting through the apertural pores 

 of adjoining chambers. In the vast majority of cases the cells 

 are arranged on the planorbuline plan, and consequently there 

 is a well-defined suture. 



I must also remark that Schlumberger's photogravure 

 (Fig. 7, Plate 3, representing a transverse section of a test), 

 does not show the double shell-wall, neither does his wood cut 

 on page 121. which I reproduce here (Plate VII, fig. 1.) 



Schlumberger's specimens were collected from the 

 Upper Eocene deposits at Bruges (Gironde). 



(Halkyard does not appear to have had personal acquain- 

 tance with any specimens of Schlumberger's Genus Linderina, 



