MUSEUM OF COMPARATIVE ZOOLOGY. 287 



fragments indicate that it must reach the largest size of any member of this 

 group. 



Pecchiolia (Meneghini, 1851, Cons. suUa Geologia Stratigr. della Toscana, 

 p. 180). Shell destitute of lunule ; much inflated ; beaks much coiled and 

 widely separated ; line of the external ligament passing under and coiled with 

 the beaks ; ossicle (not seen, but must have been enormous and like that of 

 Verticordia, but flatter) ; right valve, hinge as in Verticordia except for the 

 depressed lunular space ; left valve ditto, but with an obtuse thickening of 

 the cardinal margin to fit behind the large cardinal tooth of the right valve. 

 Type P. argentea Mariti, fossil in the Vienna basin and Italian tertiaries. No 

 recent representative known. 



This and other sections of Verticordia have been referred to Hipjjagus (Lea, 

 1834). But from a study of authentic specimens received froui Dr. Lea, I find 

 the type of Hippagus to belong to the Mytilidoe. The external sculpture, the 

 position of the muscular scars and ligament, and the general form and texture 

 of the shell in Hippagus agree perfectly with Crenella, from which Hippagus 

 difi"ers only in having the beaks slightly more twisted than the common recent 

 species of Crenella, and in having the shell thicker, so that the external sculp- 

 ture does not crenulate the edge. Compare the original figure of Hippagus 

 with Modiola cinnamomea Chemnitz, or a specimen with a shell of equal size 

 of Crenella decussata, and it is easy to come to a conclusion. 



I have been able to study a fine series of Pecchiolia in the Jeff"reys collection, 

 and observe that one must be certain of the perfection of the specimen if he 

 would avoid being led into error, for the fossil shell scales off in such a way as 

 to alter the hinge entirely, and yet not appear defective. The scars of the in- 

 ternal cartilage are wonderfully large and deep, and if, as is probable, it bore 

 an ossicle , this must have been enormously large. 



Haliris Dall. Shell globose, ossicle short, squarish ; lunule present, not 

 deep ; right valve with hinge teeth as in Trigonulina ; left valve with (in the 

 adult) a small but distinct cardinal tooth and a short stout lateral tooth near 

 the umbo ; lunule not produced ; adolescent or young shells with the dentition 

 obscure or imperfect. Type Verticordia Fischeriana Dall. Gulf of Mexico in 

 deep water. 



To this group belong V. trapezoidea Seguenza, and perhaps his V. granulaia, 

 which I have not seen, and which has not been well figured. These have been 

 perhaps too hastily united by Dr. Jeff'reys. 



The genus Mytilimeria, whose position has been somewhat debated, unques- 

 tionably belongs in this family. The mantle is closed except for the two large 

 siphonal openings, which are, on a large scale, similar to those of Lyonsiella, 

 and a minute slit for the very small phalliform foot, which has a shallow pos- 

 terior sulcus and a slightly enlarged glandiform tip. The mantle margin is 

 thick and plain except about the siphons. There are two rather good-sized 



