54 The Upper Cretaceous Deposits of Maryland 



ramus and Exogyra, though not restricted to the Cretaceous, are char- 

 acteristic of it, while Gryphwa and Trigonia reach their culmination in 

 the middle and upper Mcsozoic. The Cretaceous representatives of the 

 more highly specialized orders, the Anomalodesmacea and the Teleodes- 

 macea, are conspicuously distinct from the later types. Of the four 

 Anomalodesmacean genera, two of them, Periplomya and Liopistha are 

 restricted to the Cretaceous; Pholadomya is distinctly Cretaceous in its 

 affinities, though it persists in greatly diminished numbers even to the 

 Eecent, while Cuspidaria was likewise initiated in the mid-Mesozoic, and 

 though wide-ranging has never been a major factor in any fauna. 



The Teleodesmacea. the most highly organized order, is much less 

 important, relativety, than in the Cenozoic faunas. The genera are more 

 specialized than in the Prionodesmacea, and many of those identified in 

 the fauna under discussion are either restricted to or characteristic of the 

 Cretaceous. The sole representative of the Cypricardiacea is the abun- 

 dant Yeniella, a typically Cretaceous genus, although persistent into the 

 Tertiary. The comparatively modern C'rassatellites is the most abundant 

 member of the Astartacean fauna, although Crassatellina and a number 

 of undeterminable species of Eripliyla, both of them genera restricted to 

 the Cretaceous, are also present. The Carditacea are represented by a 

 single rare species of Y enericardia, the Lucinacea, by a rare Myrtcea and 

 the Bancocas Phacoides noxontownensis, together with the prolific Cre- 

 taceous Tenea of rather uncertain affinities. Cardium is abundant during 

 the late Mesozoic, as it is during the later Cenozoic. The Venerids are 

 rather primitive; the prolific Cyprimeria, and Legumen do not survive 

 the emergence at the close of the Mesozoic, while the more modern 

 Dosinia, Cyclina and Meretrix are known from less than a dozen indi- 

 viduals. The prolific species of Tellinacea are all of them included under 

 genera restricted in their distribution to the Cretaceous, i. e., Tellinimera, 

 JEnona and Linearia, although the true Tellina is also present. Neither 

 of the Solenacean genera, Leptosolen or Solyma, survives the close of the 

 Mesozoic, nor does the prolific Cymbophora, the single representative of 

 the Mactracea. Both of the Myacea, however, Corlula and Panope, are 

 abundant in the Tertiary and Eecent seas, as well as in the Cretaceous, 



