140 



UNITED STATES NATIONAL MUSEUM BULLETIN 29 6 



Dimensions: About 1.5 X 0.5 mm, not counting the thickness of 

 the flange. Slit length reaches about 2.7 mm, but may be much 

 shorter. The flange which is usually present is thick, swollen, and of 

 about 0.5 mm in maximum width. 



Rogerella mathieui Saint-Seine, 195.5a, page 300 



Diagnosis: Fossil aero thoracic an burrows with aperture straight 

 or arched, widening regularly without two distinct parts. Flange 

 thin, fragile, usually absent. 



Distribution: It is found in echinoids of the middle Jurassic, 

 invading lamellibranchs, belemnites, and corals in the Upper Cretace- 

 ous, persisting sporadically in the Miocene and Pliocene. Anglo- 

 Parisian basins. 



Dimensions: Aperture 1-2 mm X 0.3-0.8 mm in length and width; 

 the burrow is 1.3-2.5 and 0.6-1.1 mm in length and width. Burrow 

 length may attain about 3 mm (var. elongata) without appreciable 

 variation in width. 



Figure 40. — Ibla idiotica Batham, 1945 

 (from Batham, 1945). ^ 



LAR 



