60 NILS ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. V. PROSOBRANCHIA. 1 DIOTOCARDIA. 
Expie!$/sal871) 1usp;rd.N6 (varisl bo D:05- 45 S3SNIHS126 OrIWE, SOK finstistoness 
shells: (!"/s 1871) many sps, max. h. 8; ap. 4; d. 9.3; wh. 5:!/e. 
Variation of the shell and the radula. 
General remarks. As to form, the shell varies in two ways: 1) towards an ele- 
vated shape and, 2) towards a more or less depressed one. As to sculpture the follow- 
ing stages may be distinguished: a) the normal sculpture, composed of rather 
coarse, flattened keels, abruptly truncated in their upper margin by a spiral im- 
pression; b) a coarser sculpture, derived from the latter by means of an additional 
shallow furrow on the keels, through which these are given a definite lower margin; 
ce) a finer sculpture, derived from the first by an extreme depression of the keels, 
so that at last only fine strie remain, which may in extreme cases wholly disappear. 
| Norway, limits h. 
La —5 | 67 19100 | max. 10 (Finmark) | 
| of variation, ap: | 2.2—3.2 | 3—4.2 | 4.1—5.6 | 5 | 
| 60 sps d. | 4,5—06.7 | 6i1—8:0)|18:s-—121 | 10.5 | 
| measured wh. |4!/2—5!/1 | 5!/4—5?/1 | 6—6!/2 | 6!/2 | 
The sculpture characteristic of Norwegian shells is the coarser spiral liration 
b); and often short longitudinal folds appear at the suture of the shells (M. undulata 
SOWERBY). NSometimes, however, the shell is entirely smooth and either of a conical 
shape (var. levior JEFFREYS), e. g. from Bergen, or depressed like var. umbilicalis, 
e. g. specimen from Bejan and Bodybet. 
Iceland. All these specimens belong to the variety 1 b, agree wholly with the 
Norwegian forma undulata, and fall within the same limits of formal variation. The 
maximal size is greater here than in Norway. Smooth specimens also occur, be- 
longing to the conical var. levior, but var. umbilicalis is not represented in the 
collections. 
Murman Coast and Kola Peninsula. These specimens agree with the Norwegian 
form 1 b; no examples of var. umbilicalis have been found. 
Kara Sea. Leche's M. groenlandica var. rudis Mörch is like the Norwegian 
shell, but somewhat lower than the specimens from Finmark, similar to the typical 
form of Spitzbergen and Greenland; besides this occur varieties 2 a—2 c (var. levigata). 
Spitzbergen, int |, 
| 4—5 ÖT | 9—10 | 13—14 18—19 9 max. 18. [8 o(AdsNNEAs ad 18. sla HeklaCoxa ) 
limits of variation; ap. | 2.3—3.5 | 3.7—4.8 | 5—6.3 | 6.5—8.8 9—10.5]| 10 9.5 | 
| 130 sps measured d. | 5—7 | 7.5—10 |10.3—13.3/14.5—18 | 19—22.4| 19.8 22.4 
wh. |49/1—5 5—5!/2 | 5!/1+—5?/4 | 5!/2—62/4 | 6!J1—6?/4 | 6?/4 6'/« 
For a few specimens the measurements fall out of these limits. Such forms 
are either extraordinarily low or exceptionally high. In the latter case they agree 
entirely with the shells from Finmark or fall out of the limits of their variation (e. 
g. specimens from Virgo's harbour: h. 15.3; ap. 7.4; d. 16; wh. 67/4 (var. 2 c). Greatly 
