1^8 SMITH : ON THE GENUS ASTARTE. 



perhaps worthy of retention, for the sculpture of that shell differs 

 in a remarkable manner from that of other species. 



The crejiulation on the margin within the valves is of 

 importance in the discrimination of species. In A. borealis^ A. 

 roUandi, A. elliptica, A. fabula, A. compj-esso, A. qiiadrans, A. 

 longirostra, A. acuticostata, A. compacta, A. mirabilis^ A. esqid- 

 malti and A. fluctiiata it is never found, whilst it is always met 

 with in adult specimens of A. sulcata^ A. crebricostata, A. nndata, 

 A.fusca, A. cfenafa, A. casta/iea, A. triangiilaiis, A. bipariita 

 and y^. viagellanica. 



C. F. Roemer* has expressed an opinion that this crenulation 

 is formed only when the animal arrives at maturity or at the 

 completion of a period of growth. Totten in 1835 iioticed that 

 the margin of the young and half-grown shells of A. castanea had 

 their "margins perfectly smooth." A. A. Gould in.1841 says "it 

 is perfectly certain, that no species of the genus is found with a 

 crenulated margin until the shell has arrived at its full dimensions 

 and the margin of the valves begins to thicken, as it always does, 

 and then, so far as my observation goes, there is always a 

 crenulated margin; so that this is a mark of maturity." 



Dr. Gwyn Jeffreys however remarks that this "is opposed to 

 my own observation (especially as regards A. triangularis).^' 

 Dr. Malm suggested that the margins were denticulated when in 

 the course of growth they met on a rib, but smooth when on a 

 furrow. This theory cannot however be maintained, for A. tri- 

 angularis produces crenules although ribless, and A. bipartita is 

 likewise notched, yet the margins can neither meet upon or 

 between the ribs, they being non-parallel with the growth of the 



* De astartum genere et speciebus, quae e saxis jurassisis atque cretaceis 

 proveniunt, Berolini 1842. Also a German translation by Dr. Ferd. Roemer 

 in Leonhard and Bronn's neues Jahrbnch fiir Mineralogie, Geognosie, Geologie, 

 &c., for 1843, pp. 58—74. 



J.C, iii., July, 1881 



