VULSELLA. 



TESTA longitudinalis^ equivalvis^ subirregularis, 

 umbonibus aequalibus. Galium cardinale^ in 

 utraque valva, prominulum^ superne depressum, 

 et fovea ligamenti conica^ oblique arcuata^ de- 

 super impressum. Impressio muscularis unica^ 

 oblonga^ versus basim testae attenuata. 



The VulsellcB^ separated from the Ostrece by Lamarck, ap- 

 pear, nevertheless, to be nearly related to them : the dif- 

 ferences, however, are such, that they cannot be re-united 

 to them ; and, indeed, they seem sufficiently distinct, not 

 only from Ostrea, but from every other Genus, and not to 

 be confounded with any, when a due degree of attention is 

 paid to the characters peculiar to each. Without further 

 preface we shall describe Vulsella, and as we proceed, we 

 will endeavour to point out the particular characters which 

 distinguish it from other genera, such as Ostrea, Crenatula 

 and others, which appear most nearly related to it. 



Shell longitudinal, that is longer, in the direction from 

 the base to the summit (using these terms in their common 

 conchological acceptation) than it is broad : the general form 

 is rather irregular, but the two valves are equal and alike, 

 in these respects, differing materially from Ostrea, which is 

 inequivalve ; and agreeing with Crenatula : the umhones or 

 beaks are also equal, but a little separatetj : between them 

 lie the decayed remains of so much of th6 ligament as is 

 no longer useful. The two valves are united at the hinge, 

 as in Ostrea, by a semi-internal ligament, attached in each 

 valve to a sub-triangular disk or facet, one of the points of 

 its triangle being close to the umbo and rather inclined to 

 one side; this disk, as in Ostrea, is tripartite, being divided 

 by two lines which divaricate from the umbo ; the central 

 portion, however, in Vulsella is hollow and forms a cal- 



