124 Studies in Geology, No. 3 



Area (Anadara) torocnsis var. crassa n. var. 

 Plate VII— Fig. 2. 



Shell much like type, but thicker and heavier. Anterior 

 margin slopes posteriorly from the hinge-line, forming with 

 it an angle of about 85°; ventral margin descends slightly 

 posteriorly ; posterior margin unknown. Beaks high, the 

 upper surface about 21 mm. above the hinge, rounded in 

 outline as viewed laterally, erect. General contour of shell 

 as in typical A. toroensis. Ribs 22 in number, from anterior 

 end to posterior keel ; thence unknown — probably 28-30 in 

 total number; rounded, tending to squarish shape, about 

 1.6 mm. broad, with equal interspaces. Growth-lines prom- 

 inent. Area very high, with many waved furrows and 

 sinuous grooves, the latter prominent near the beaks and the 

 former near the hinge. Hinge-line narrow, with many fine 

 teeth. Length, 53; height, 51; (semi) diameter, 28.5; 

 length of hinge, 41.5 mm. 



The differentiation from the typical Area toroensis is 

 based on variations which would certainly have specific value 

 if the characters were more constant. As matters stand, 

 with some heterogeneity within the species of A. toroensis, 

 the likelihood of very close association between the true 

 form and this variety is high, and although the obviously 

 larger area, proportionally broader ribs, and incurving ven- 

 tral surface of this form offer striking difference, and seem 

 to demand distinction greater than that implied by the assign- 

 ment of varietal rank, the probability of close relationship 

 precludes the use of a specific name until more material 

 shows the variation to be thoroughly constant. 



The variety is very close to A. Hehteli Deshayes, figured by 

 Hoernes ^-^ from the Miocene of the Vienna basin. The only 

 difference lies in the area, which in fiehtcU is furrowed regu- 

 larly, the furrows being evenly spaced, whereas in erassa 



'''Abh. k.k. geol. Reichs., Bd. 4, p. 331. pi. 43, figs. 3, 4, 5, 1870. 



