28 SPECIES OF THE SYSTEMA. 
answers to the account of this species, which, having been 
described at length in the ‘ Fauna Suecica,’ and fairly enough 
delineated in both the ‘ Historia’ of Lister and the ‘ Tentamen 
Methodi’ of Klein, has been recognised with facility by concho- 
logical writers. 
slpa pera. 
Our author intended (had life been spared him) to have re- 
moved the above shell from Mya, and to have placed it along 
with his Mytilus bidens and ungulatus in a proposed new genus 
Perna, the equivalent to the restricted Mytilus of Lamarck. 
The Mytilus perna of authors (Schrét. Einleit. Conch. vol. 1. 
pl. 7, f. 4) is marked for this species in the Linnean collection, 
and answers admirably the requirements of the description. 
The reference to Argenville is correct. 
Siva bulsella. 
Our author did not possess this comparatively scarce shell. 
The ‘Museum Ulric’ enables us to recognise it in the Vulsella 
lingulata of Lamarck (Sowerby, Genera Shells, Vuls. upper 
figs.). 
Mpa arctica. 
The Miatella (Saxicava) arctica of modern writers (Turton, 
Dithyra Brit., pl. 2, f. 12) is still preserved in the Linnean ca- 
binet, and alone of its contents agrees with the excellent 
description in the ‘Systema.’ Our author meditated the re- 
moval of the species to Solen, and in his manuscript had 
written “ subedentulo ” in place of “‘ edentulo.” 
