JURASSIC FOSSILS FROM RIKUZEN. 13 



6. PERNA RIKUZENICA n. sp. 



PI. I. Fig. 1. 



Several specimens of a large quadrate Perna were obtained, 

 which are however more or less broken. The figured specimen 

 has both valves preserved and measures 8 cm. long, 6 cm. broad 

 and 3 cm. thick. The shape of the shell, which is decidedly 

 four-sided and has the anterior border concave resembles that of 

 Perna rugosa Goldf. figured by Morris and Lycett in their 

 Ponograph of the Mollusca of the Or eat Oolite {pi. XIL, fig. 1 ; 

 pi. XIV., fig. 16). But on a closer examination our shell differs 

 in several points from the European. In the first place our shell 

 is a little more inflated ; in the second place the greatest inflation 

 lies very close the anterior border, so that the surface descends 

 abruptly to it, while towards the posterior border the slope is 

 very gradual ; and in the third place the surface is not rugose, 

 being marked only by fine concentric lines of growth. 



Localitv : — Hosoura. 



