LAMELLIBRANCHIATA. 6l 



of ••Mod.sii.bstriata" , so small is the difference between them"). Mod.discors (PI. Ill, figs. 6a — b) is on 

 the whole a more oblong form; this is the essential difference. But whilst maintaining, that Mod. Iccvigata, 

 Mod. substriata and Mod. discors are identical specifically, I may yet emphasize that in their typical 

 shape they are representatives for just as many special forms and must not be summarily thrown together. 



Furthermore, the form discors, as I know it from Danish waters, is also not a little variable; 

 frequently the posterior area is distinctly striated, but sometimes it appears almost smooth (cf. var. 

 scmilcrvis Jeffreys, Brit. Conchol. II, p. 127); I have even before me at this moment a specimen from 

 the Great Belt (Sveudborg), which combines a striation such as we find in substriata with the form of 

 a typical Iccvigata, or on the whole shows a great resemblance to a very young Mod. IcBvigata. 



In conclusion I ma\' quote some little known observations regarding the biology of this species. 



In his paper "Om Ueens-Muslingen" (i.e. M. discors \ds. Iccvigata and substriata) O. Fabricius') 

 writes as follows: "This Bivalve I have found to be of common occurrence in Greenland, where it is 



called Bibibiarsuk ; I do not know the certain origin of this word one might be inclined to think, 



that the Greenlauders have found this name suitable for the whistling or hissing noise, this Bivalve . . . 

 produces when it has stood for a long time closed at ebb-tide for want of water and then with the 

 coming of the flood begins to open again. It is attached by its fine silk (byssus) to large stones or 

 rocks in the sea, the largest end sticking upwards, the open side turned towards the stone or foreign 

 body, to which it is attached. It lives preferably so far from the land, that it does not become dry 

 except at spring-tides when the greatest ebb occurs. On the blind rocks out to sea, therefore, it is 

 most uumerous .... When its silky hairs have been broken by the waves or other cause, I have seen 

 it stretch out its foot, attaching it to the solid rock, elongating and contracting it, and thus push 

 itself forwards .... the fattest and largest are found on clay bottom " 



In a manuscript left by H. P. C. Moller we find: "It occurs everywhere in quantities on the 

 coast of Danish West Greenland and especially where there is shallow water, partly on Laminaria, 

 more rarelv on Fucus, partly among the string-like algal forms and among stones, down to a depth 

 of 20 fm. or still deeper, e. g. at Nennortalik, Godhavn; I have taken it in 30 fm. opposite Nepisene 

 at a distance of 8 Danish miles from the coast." 



And in a notice: "Ueber Aiytilus discors" lap. Steenstrup makes the following remarks on 

 Modiolaria discors var. laevigata at Iceland: ". . . . Noch raehr zeichnet sich diese Muschel durch iliren 

 selir ausstreckbaren Fuss aus, welcher ihr erlaubt, die Byssusfaden iiicht nur um die Seiten der Schalen, 

 sondern audi iiber den Riicken derselben herumzuffihren; dadurch kann sie sich ganz mit einer 

 Byssushiille umgeben oder sich wie in einem Byssussack verstecken. Die Enden der ausseren Bys- 

 susfaden werden auf kleinen Steinchen, Muschelschalentriimmern und dergleichen festgeheftet, so dass 

 der Byssussack ganz einem Steinhaufchen gleicht; die innere Wand der Byssushiille ist dagegen selir 

 glatt, aus dichtliegenden, sich kreuzenden Byssusfaden gebildet, und schliesst sich den Muschelschalen 

 ziemlich dicht an. Nur das hintere Ende der Hiille hat eine Oeffnung, sonst ist sie ganz geschlossen. 

 In seichten ]\Ieeresbusen, in welchen der Boden mit grobem Sande und Grande bedeckt war, hat S. 



1) Leche has obviously been of the same opinion, as he writes (I.e. p. 451), that the Mod.discors from Kiel Bay, 

 sent him by Mobiiis, cannot be specifically distinguished from Mod. Iievfs Beck; Leche refers to this in connection with the 

 fact, that G. O. Sars had erroneously identified Mobius' Mod.discors with Mod. corrugata Stimpson. 



2) Nye Samling af det Kgl. Danske Videnskabernes Selskabs Skrifter, 3. Deel, 1 788, p. 453. 



