112 



LAMELLIBRANCHIATA. 



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



with the more or less folded varieties of Astarte borealis Chemn. ^^A. seiitisiilcafa Leach" etc.jM; 



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



Locahtv Length Height Breadth 



Length Length 



Seydisfjordr 32.25 """'. 23.25 "'"\ 72.1 % q.5 "'"". 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. cUiptica 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 such dimensions as the following: 



Height Breadth 



Length Height ^ — Breadth 



Length Length 



31.25"'". 26.25 "'"V 84% 15.2'""'. 48.6% 



27-25 - 23.25 - 85 - 14.2 - 52.1 - 



It has obviously been sitch specimens as these, which have led Leche to set up the variety crassa^]. 

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

 not rareh', 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 d(prrssa (for specimens from Hekla Havn3). 



Height Breadth 



LocaUty Length Height Breadth 



Length Length 



Cape Daltou 29.5 """'. 21.5 "'"'. 72.9 % 12.5 "'"'. 42.4 % 



— — 29.5 - 21.5 - 72.9 - 11.5 - 39 - 



Hurry Inlet 27 - 20 - 74.1 - 9.5 - 35.2 - 



Hekla Havn 23.5 - 16 - 68.i - 8 - 34 - 



— — 22.5 - 16.5 - 73.3 - 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 ^{. rlliptica (from the Faeroes), seen from the side and from above. 



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



2) Leche: Ofversigt ofver de af svenska expeditionerna till Nowaja Semlja och Jenissej 1S75 oeh 1876 insamlade 

 hafs-mollusker, p. 19, PI. I, figs. 3 a— b. Kongl. .Sv. Vet. Akad. Handl., Bd. 16, No. 2, 187S. 



3) L. c. 1895, p. 72, PI. L figs. 5—7- 



