112 



LAMELLIBRANCHIATA. 



on the umbona] area. Such specimens may have great resemblance and are certainly often confused 

 with the more or less folded varieties of Astarte borealis Cheinn. ^A. semisulcata Leach" etc.) 1 ); 

 the large ligament projecting over the shell of the last-named as also the more or less fibrons or 

 frayed structure of the periostracum makes the separation in general quite easy. -- The form also 

 appears to be very variable, both in relative height and breadth, as will be seen from the following 

 measurements. 



. , Height Breadth 



Locality Length Height Breadth 



Length Length 



Seydisfjordr 32.25""". 23.25 mm . 72.1 % 9-5 mm - 29.5 % 



31.25 - 21.75 - 69.6 - 12 38.3 - 



Nordfjordr. 32.5 - 23.25 - 71.5 - 11.75 - 36.2 - 



Dyrafjordr 31 - 23 - 74.2 - 14 - 45.2 - 



Talknafjordr. 32 25.5 - 79.7 - 14 - 43.8 - 



At West Greenland A. elliptica is subject to similar variations as at Iceland. In regard to 

 form there are specimens which are even higher and more vaulted than those which go to an 

 extreme in this direction at Iceland, so that we find snch dimensions as the following: 



Height Breadth 



Length Height Breadth 



Length Length 



31.25 n,m . 26.25 n,m . 84% 15.2 mm . 48.6% 



27.25 - 23.25 - 85 - 14.2 - 52.I - 



It has obviously been such specimens as these, which have led Leche to set up the variety crassa 2 ). 

 At East Greenland A. elliptica usually appears with folds right down to the ventral margin; 

 not rarely, however, they cease about the middle of the shell. — With regard to the form, this is 

 remarkable on the whole for its elongation, as will be seen from the measurements below; Posselt 

 for this reason set up a special variety depressa (for specimens from Hekla Havn3). 



Height Breadth 



Locality Length Height Breadth 



Length Length 



Cape Dalton 29.5 mra . 21.5 mm . 72.9 % 12.5 mm . 42.4 % 



29.5 - 21.5 - 72.9 - 1 1.5 - 39 - 



Hurry Inlet 27 20 - 74.1 - 9.5 - 35.2 - 



Hekla Havu 23.5 - 16 - 68.1 - 8 - 34 - 



22 -5 16.5 - 1 i. i - 7.75 - 34.4 - 



The following figures on PI. IV may serve as illustration of the varying form and sculpture 

 in Astarte elliptica^ mentioned in the foregoing: 



Fig. 4 a and b represent a typical A. elliptica (from the Fseroes), seen from the side and from above. 



1 For example, both Morch and Posselt have made mistakes in this direction. 

 Leche: Ofversigt ofver de af svenska expeditionerna till Nowaja Semlja oeh Jenissej 1S75 och 1S76 insamlade 

 hafs-inollusker, p. i 9 , PI. I, figs. 3 a b. Kongl. Sv. Vet. Akad. Handl., Bd. 16, No. 2, 1878. 

 I c. [895, ]>. 72. PI I, figs. 5—7. 



