BRACHIOPODA. 



153 



Genus CRANIELLA, (Ehlert. 1888. 



PLATE IV I, FIGS. 1-10. 



18S8. Craniella, Q^hlert. Bull, de la Soc. d'Etude-s scieiitif. d'Ang:nvs, p. 37. 1887. 

 1889. Craniella, K.\yser. Abhamll. der KiJnigl. Preuss. geol. Landesanstalt, Nnue Folg-e, Heft i, p. 6"i. 

 Crania, in ]iart, of several authors. 



Diagnosis. " Shell somewhat irregular, outline subcircular or subquadrangu- 

 lar. Ventral valve thin, adhering by its entire surface ; dorsal valve conoidal, 

 more or less elevated ; apex subcentral, posterior ; interior of the dorsal valve 

 without a well defined border ; impressions of the 

 adductors large, very distinct, four in number, of 

 which the posterior two are quite distant, the two 

 subcentrals somewhat smaller, closely approximate 

 or even confluent; from near each of the posterior 

 impressions starts a vascular sinus, which is broad, 

 strongly sinuous near its point of departure, nar- 

 rowing gradually in following the contour of the 

 valve, emitting from its marginal side dichotomiz- 

 ing secondary branches." (CEhlert, loc. cit.) 



Type, Craniella Meduanensis, (Ehlert. 



Observations. With the peculiar sigmoid vascular sinuses in the upper valve 

 as a distinctive character, we are disposed to regard this genus as well grounded. 

 This character is observed in an interesting species, Craniella Ulrichi, sp. nov., 

 from the Trenton limestones at Minneapolis, Minnesota, and in the common 

 Crania HamilionicE of the Hamilton shales, and undoubtedly will be found to be 

 far more generally distributed as the interior features of the palaeozoic Cranias 

 become better known. To the degree of attachment of the lower valve we 

 should ascribe less importance than does Dr. OEhlert. The Trenton species 

 mentioned is sometimes attached and evidently as often free, while C. Hamiltonice 

 appears to be, like C Meduanensis, invariably adherent by the entire surface of 

 the lower valve. 



Fif;. 7-. CranifUa MejJuanpnsis. 



After CEHI.EUT. 



Internal cast of upper valve. 



