LAMELLIBRANCHIATA. 



63 



Remarks. Great uncertainty prevails 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. 

 substriata Gray ("M. Icevis Beck"). From a close investigation I have comi 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. 5c) but showing under the lens a shagreen-likc wrinkling 

 the surface, as shown in fig. yd on PI. Ill (cf. also Krause: Ein Beitrag zur Kenntniss der Mollusken- 

 Fauna des Beringsmeeres, 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 



Locality 



shell shell Length shell Length 



Greenland 15.75 mm - IO ram - 63.5% 7.5 """. 47.6 



14-5 " 9-5 - 65.5 - 7.5 - 517 



1+25 - 9 " 6 3- 2 " 7-5 - 5 2 - 6 " 



12.3 - 775- 63 - 7 56.9 - 



8 - 5.75 - 71.9 - 4-75 - 594 - 



Spitzbergen 26.5 - 17 64.2 - n - 41.5 - 



24 15.75 - 6 5- 6 - 10.25 - 42-7 - 



22.5 - 14.75 " 6 5- 6 - I0 " 444 - 



18.75 - " - 6 4 - 8 " 42-7 - 



13-75 - 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 - 55.0 - 



8.25 - 5.75 - 69.7 - 4 - 48-5 - 



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



Modiolaria nigra Gray. 



Modioli 1 nigra Gray, Parry's first voyage, Suppl. to App., [824, p. 244. Crcriclla nigra Torell, 



Spitsbergens Molluskfauua, 1859, p. 130. ■ Modiolaria nigra Jeffreys, Brit. Conch ol. II, 

 1863, p. 128, PL 28, fig. 4; Gould & Binney, Rep. Invert. Mass. [870, p. 190, fig. 487 (juv.) & \& 



Modiola discrepans Moller, Ind. Moll. Groenlandise, 1842, p. 10. Modiolaria striatnla Beck, in Gai- 



mard, Voyage de la Recherche, PI. 17, figs, ia f; Amtl. Bericht 24. Versamml. deutsch. Naturf. 



Archiv fur Naturgeschichte, [885. 



