LAMELLIBRANCHIATA. 



63 



Remarks. Great uncertainty prc\ails among authors regarding Modiolaria corrugata ; often it 

 is called a "transitional form" to other arctic species of Modiolaria^ and especially to M. discors L. var. 

 subslriofa Gray ("M. Icrvi's Beck"). From a close investigation I have come to the result, that 

 M. corrugata is an exceedingly well defined species. M. corrugata certainly shows some resemblance in 

 habit to M. discors var. substriata., but is readily distinguished from this by the middle area being not 

 smooth or simply striated (cf. PI. Ill, fig. 5 c) but showing under the lens a shagreen-hke wrinkling of 

 the surface, as shown in fig. jd on PI. Ill (cf. also Krause: Bin Beitrag zur Kenntniss der MoUusken- 

 Fauna des Beringsnieeres, p. 19) '). A similar kind of surface is also found, however, in M. nigra; but 

 in the latter the posterior, striated area grades evenly over into the middle area, whereas in M. corru- 

 gata the middle area appears depressed along the boundary line towards the posterior area, as in M. 

 discors; further, in M. corrugata the radial striation is coarser, the shell more ventricose (cf. measure- 

 ments of M. corrugata with those of M.nigra) and with more prominent umbones. In regard to shape, 

 moreover, M. corrugata is rather variable, as will be seen from the following measurements of a number 

 of specimens: 



Length of Height of Height Breadth of Breadth 



^'^^ ' ^ sheU shell Length shell Length 



Greenland 15.75 """• 1° "'". 63.5 % 7-5 ""■• 47-6 % 



— 14-5 - 9-5 - 65.5 - 7-5 - 517 - 



— 14-25 - 9 - 63.2 - 7.5 - 52-6 - 



— 12.3 - 7-75- 63 - 7 - 56-9 - 



— 8 - 5.75 - 71-9 - 4-75 - 59-4 - 



Spitzbergen 26.5 - 17 - 64.2 - n - 4i-5 " 



— 24 - 15-75 - 65.6 - 10.25 - 42-7 - 



— 22.5 - 14.75 - 65.6 - 10 - 44.4 - 



— 18.75 - 12 - 64 - 8 - 42.7 - 



— 1375 - 8.75 - 63.6 - 5.75 - 41-8 - 



— 13.25 - 8.8 - 66.4 - 5.75 - 43-4 - 



— 13 - 8.75- 67.3 - 5.5 - 42-3 - 



8.5 - 6 - 70.6 - 4.75 - 55-9 - 



— 8.25 - 5-75 - 69.7 - 4 - 48-5 - 



Kara Sea 21.5 - 13 - 60.5 - 9 - 4i-9 " 



Modiolaria nigra Gray. 



Modiola nigra Gray, Parry's first voyage, Suppl. to App., 1824, p. 244. — Crcvclla nigra Torell, 

 Spitsbergens Molluskfauna, 1859, p. 130. — Modiolaria nigra Jeffreys, Brit Conchol. II, 

 1863, p. 128, PI. 28, fig. 4; Gould & Bin ney. Rep. Invert. Mass. 1870, p. 190, fig. 487 (jnv.) &488. 



Modiola discrcpans Moller, Ind. Moll. Groenlandise, 1842, p. 19. — Modiolaria striatula Beck, in Gai- 

 mard. Voyage de la Recherche, PI. 17, figs, i a— f ; Amtl. Bericht 24. Versamml. dentsch. Naturf. 



I) Archiv fiir Xaturgeschichte, 1885. 



