296 Dr. Philippi on Paiidorina coniscans. 



slight incurvation of the mantle can be recognised. From 

 this it appears that Pandorina^ is certainly the most nearly- 

 allied to Pandora ; but on account of the internal bone of the 

 ligament, the absence of teeth to the hinge, the gaping of the 

 posterior side, this genus also joins on to Thracia, which (at 

 present I can only compare Thr. phaseolina or Tellina papy- 

 racea, Poli) is distinguished by a short external ligament rest- 

 ing on distinct nymphae, by a far more decided incision be- 

 neath the apex and a deeper incurvation of the mantle ; here 

 too the left shell is the more convex, as in Corbula, not the 

 right one, as in Pandora and Pandorina. But Pandorina is 

 distinguished from both these by the longitudinal stria, which, 

 as far as I am acquainted, do not occur in them or even in 

 the whole family of the Myce and Corbulae. 



From this last circumstance, the complete absence of hinge 

 teeth, the double ligament, the brittleness of the shell, and lastly 

 from the thinness of the epidermis which covers the whole 

 shell, Pandorina brings to mind the singular genus Galeomma, 

 which is truly very diiferent at first sight, from the equality 

 of the shells and the wide gaping of the ventral side, as also 

 from the existence of only one tube, or if we choose the second 

 obliterated, as in Solenomyaf ; nevertheless, I believe that Ga- 

 leomma is more nearly allied to this genus than to any other. 

 M. Deshayes, who was only acquainted with the mere shell, 

 classes it with Glycymeris, which genus however differs very 

 considerably by its very thick epidermis, rather reminding us 

 of Solenomya, its strong prominent nymphae, its small foot, 

 its slightly slit mantle, and the long thick cohering siphons. 



There are at present therefore six genera with a little bone 

 in the ligament: ^/^«/i/^«, Lamarck, Desh.; Periploma, Schum.; 

 Ost€odesma,T>es,h.; Thracia, Lteach; Pandorina, Scacchi, which 

 all belong to the family of the Myacece, to which Deshayes 

 with good reason unites the Corbulacece ; and Cleidothcerus, 

 Sow., which is allied to the Chamce, 



* See note in the following article, p. 305. 



f On the outside of Solenomya where we expect to find the anal tube, it 

 presents a circle of papillae, which is however not perforated, as is very accu- 

 rately stated by Sr. Scacchi. I'his explains why M. Deshayes has ascribed 

 two siphons to the Solenomya, 1 on the contrary only one. We both saw 

 correctly, but not accurately enough. 



