_"f OLAF HOLTEDAHI.. [SEC. ARCT. i:xi-. ri?.\M 



Lissatriii>(i xt'lieii uov. sp. 



IM. VII, figs. D-12. 

 This highly interesting fossil is no doulit the one mo.-.l abundantly 



O . CJ 



occurring in tin' material. A great numher of free specimens are pre- 

 senl, and some pieces of a brownish grey. very fine-grained limestone 

 filled with it, give us a good idea of the abundance of the specimen 

 in the rock. 



I posses specimens of very different size and the outer form changes 

 with the si/e. The adult specimen usually reaches a length of about 

 2 cm., a width of 1,8. The thickness varies much, in globose types it 

 amounts to 15 16mm., in flatter ones to 1213. The outline of the shell 

 seen from above also varies considerably; sometimes it is evenly rounded, 

 oval, but with the umbonal region more sharply lined and prominent. 

 Most specimens have a more polygonal outline, the margins on both 

 -ides of the beak straight, meeting at the beak at very obtuse angles. 

 From these lines the lateral margins turn abruptly forwards, then gently 

 curve towards the medium-line and meet at the anterior end in a nicely 

 rounded curve. The greatest width of the shell is generally at a point just 

 In-hind the centre. The convexity of the specimen varies, as mentioned above 

 greatly, the strongest convexity in the posterior part. Specimens with 

 relatively flat ventral and convex dorsal valve remind us as to the general 



* 



form, apart from the character of the surface, very much of small Atrijfxi 

 reticiilftri*. A> to the presence of a sinus and fold, there is consider- 

 able variation to be seen. In fact the specimens from the two local- 

 itie>. where the specimens were found show a slight difference in this 

 respect The specimens from Seal Hay show m the anterior third, 

 a more or less well marked sinus and fold. In some cases the 

 ventral valve in the front runs out into a tongue-shaped process. In 

 the more numerous -,pecimen> In. in the Reindeer Valley we very rarely 

 -e a real depressed sinus at all. What often conveys the notion that a 

 sinus is indicated, is the fact that the margin in the front makes a 

 -liuhlcnrve upward.-, and forwards in every mature shell. 



The HI-IIMS Lisslr>tixi |li- = smooth) is propoM-d by Dr. \\ . II. TwENHOFEl 



in tlic mann-M-ripl "I' a --lill iin-printrd \\<>rk mi tin- ( )r<lo\ ician and Silurian 

 Kamia^ i.f tin- . \nlirnsli Nand near Ihr Month of Hit- St. Laurence Hivn in 



I .., -I. i n i laii.-tdii. II is l.a>rd i. n a small externally ^K/iyrts-like brachiopod, which 



in iK inlrrnal cliaracliT-. iiLjrt-cs willi a true Atr/n>n. (< it-mil y |>" /,/.s-.sv/r//;m 

 TUIMI. iniv. s|i . Irnin /HIM- '.', <>[' Ilic .Inpilrr lii\rr fdriiiiitiiui "f lli<- 

 i-li -M'l-lioii. the i-ijuivalcnt of tlir (ilinlon). 



