287 Bulletin 5 17 



Say 071 Shells, c~'c. 39 



undergone much apparent change, exceptmg that the lamel- 

 lary increments are readily separable and ver)' friable, the 

 epidermis also is wanting. 



It is the same species of shell as that described and figur- 

 ed by Collini in his Journal p. 10, ph 6. fig. i. under the 

 name of Ostreiim polyleptogingliinuDi .• and also anon3^mous- 

 ly by Parkinson Organ. Rem. vol. 3, pi. 



The teeth of one specimen, in the possession of the 

 Academy of Natural Sciences, are obsolete. 



Collini says, it is often perforated by sea insects ; our 

 specimens are also penetrated, but the cavities are formed 

 by an ampullaceous Pholas, which in reality may be the 

 same as those which that author alludes to, by the term sea 

 insects ; it may be thus named and described. 



Pholas ovalls. 



Tube equal, entire and rounded at base, and gradually 

 attenuated towards the anterior termination. Sliell subo- 

 vate, dehiscent ; valves with crowded, acute, elevated, trans- 

 verse lines, somewhat decussate witli longitudinal slightly 

 indented ones, a more conspicuous, longitudinal, indented 

 line before the middle, posterior basal margin smooth ; 

 within equal, the posterior basal margin distinguished by a 

 slight undulation. - 



This is not, strictly speaking, a JViolas, inasmuch as it is 

 included in a tube ; but in other respects it corresponds 

 very well with the species of that genus, as far as I can judge 

 from incomplete specimens, not having seen the accessory 

 valves. It will not agree with Teredina Lam. as its valves 

 are concealed by the tube ; by wliich character it is assim- 

 ilated to Fishdana, but from this genus also, it is distinguish- 

 able, by the form of its valves, and most probably, b}' being 

 destitute of the anterior, crustaceous, branchial appendages 

 or valvules, though it is proper to observe that the anterior 

 extremities of the tubes (which contain these parts in fistu- 

 lana, teredo, &c.) are deficient in ray specimens of P. ovalis. 



In the somewhat compact earth which was included be- 

 tween two fragments of the valves of the abovementioned 

 Perna, were a few interesting shells, some of which are per- 

 fectly firm and entire, others, although to all appearance 

 similarly circumstanced, are extremely friable, and even 



[A. J. S., 1st Ser., Vol. II.] 



