29 



1852. p. 578 (a work which I have not had occasion to see). The type of this genus is Cliama 

 argtntea Mariti (1797) = Chama? arietina Brocchi (1814) a Miocene fossil. The Synonyms of 

 this genus are: Hippagus Phil, (non Lea) and Verticordia Searles Wood (Trigonulina d'Orb). 



If we compare the characteristics noted by the different authors (e. gr. the Brothers 

 Adams, Chenu, Woodward) for the above-named genera, we shall find some apparently very 

 essential discrepancies, which justify the assumption that not all the forms thereto referred 

 really belong together. This applies especially to the hinge, and also to the proportion be- 

 tween the two valves, which the authorities mentioned represent as equal, while in our nor- 

 thern form they are evidently unequal. Both these points are, as is well known, usually re- 

 garded as having generic significance. Jeffreys has however communicated to me that he 

 looks on the typical form P. Argentea Mariti, and also P. acuticostata (Hippagus) Philippi ' 

 as undoubtedly belonging to the same genus as the northern form here described. With 

 respect to the latter of these two species, Philippi states indeed like the other authors, 

 that the shell is aequivalve; and further he does not mention the peculiar movable ossicle 

 lying between the hinge-borders of both valves; but both these points may easily have escaped 

 his attention, as he only had occasion to examine 2 single (left) valves. In the outline of 

 the shell, our species has no great resemblance with the P. acuticostata Phil., which is roun- 

 dish or heart-shaped with strongly projecting ribs and dentated edges. But it is more like 

 the Verticordia parisiensis Deshayes^ from the chalk at Grignon, and V. leana Desh. from 

 the chalk at Monchy ', which are both oval (longitudinally) ; but the first has thin, yet pro- 

 jecting ribs, and therefore dentated edges; the latter on the contrary has no ribs, and there- 

 fore smooth edges like our northern species, which is distinguished from both by its rhom- 

 boidal shape, and by the posterior nearly straight side or edge being much higher than the 

 anterior rounded side. 



The animal of the Pecchiolia is, as above stated, liitherto unknown ; for which reason 

 it has been referred to various families, only according to the presumed similarity of the 

 shells. The Brothers Adams, like Chenu, refer it to the family of theTrigonida;; Philippi, to 

 the family Gardiidije; Woodward", to the family Cyprinidaj. With regard to the shell of our 

 species, it presents two characteristics — namely that its valves are unequal (the right larger 

 than the left) and that its ligament contains a loose ossicle, — which are foreign to the 

 above-named families, but exist in the family Anatinidce (incl. Pandoridse) to which it therefore 

 appears to be referable; although its shell does not, as in these, gape at both ends, nor has 

 any external ligament. As to the animal, it agrees with the Anatinidai in having both lobes 

 of the mantle united, with only one opening below and in front for the foot, and the foot — 

 as in some of the Anatinidas (Lyonsia) — furnished at its basis with abyssus; but its Siphons 



' Fauna MoUuscorum rcgni utriusque Siciliie. 2. pag. 42. tab. XIV. fig. 19. 



^ Chenu. Manuel de Concliyliologie- 18li2. Vol. 2. fig. 340. 



' Ibidem, fig. 842. 



* Manual of the MoUusca 186G. p ."104. 



