144. 日本産の<I>Atrypa</I>に就いて

Two external casts of Btachiopoda found by the writer early in this year in a trachytic tuff of the Nakazato Series developed at the south-western foot of Takainari-yama, Hikoroiti-mura, Kesengun, Iwate-ken, are identical with Atrypa desquamata SOWERBY, the well known Middle Devonian fossil, of world wide, distribution. The following is the short description of this fossil:<BR>Shell more or less wider than high, squarish in outline, somewhat shouldered at cardinal extremities, probably widest along hinge line, ornamented with radiating ribs crossed by well marked growth lines. Ventral valve moderately convex, with slight median depression in front, dorsal valve much inflated, being more convex than ventral valve. Radiating ribs most marked near umbonal part, thence gradually weaking to frontal region, with the increase in number by successive intercalation of new ones; five of them counted in 5mm. Growth lines concentrical, distinct, becommiug finer towards cardinal extremities, six to seven of them counted in 5mm near umbonal region. Hinge line long and straight. Area, muscular impression and brachial structure unknown. Width 27mm and height 25mm<BR>Of the three mutations distinguished by GRABAU in the Chinese forms of Atrypa desquamata, mut. kansuensis GRABAU, particularly the figured specimen from the Mlaoerhchuan bed of Kamm province approaches most closely the Japanese form, but the latter differs from the former by having better developed concentric growth lines similar to the British or west European Atrypa desquamata and by being more shouldered at cardinal extremities. To this Japanese form, a new name japonica is here proposed. Reg. No.65468.