NOTES AND EXPLANATIONS. 



(JURASSIC.) 



891 = CAMPTONECTES, Agassiz MSS. Example Pecten lens, 



SowERBY. Also includes Pecten beUistriatus,Meeh, Proc. Acad. 

 Nat. Sci. July, 1860, 311. 



The name Camptonectes lias been adopted by Prof. Agassiz 

 for a group of Jurassic and Cretaceous species, several of wliich 

 have been confounded under the name Pecten lens. These 

 shells are subequivalve, compressed, lenticular, and closed all 

 around. They have generally small compressed ears, and a 

 short edentulous hinge ; byssal sinus under the anterior ear of 

 right valve deep, well defined. Surface ornamented with fine, 

 very regular, closely arranged, often sub-punctate, radiating or 

 sub-divaricate strise, which curve gracefully outwards on each 

 side. 



This genus is known to be represented by at least one unde- 

 scribed species in the Cretaceous beds of New Jersey. It will 

 include a few species, such as Pecten cottaldinus, D'Orbigny, 

 upon which the radiating striae are nearly or quite obsolete. 

 892 = Pecten extenuatus, Meek & Hayden, Proc. Acad. Nat. Sci. May 

 1860, 184. 



895 = Avicula ? curta, Hall, Stansbury's Rept. Exped. to Great Salt 



Lake, 1852, 412. See Am. Jour. Sci. March, 1864, 212. 



896 = OXYTOMA, Meek. Type Avicula Munsteri, Bkonn, Leh. 



Zeitsch. 1829, 76. 



The shells of this group differ from the living typical Pterin 

 (^= Avicula), in having a much more deeply and sharply de- 

 fined byssal sinus. They are also less oblique, more distinctly 

 inequivalve, and usually more strongly costate, particularly on 

 the left valve, around the pallial margins of which the cost?e 

 sometimes terminate in projecting spines. This type forms a 

 transition from the true Pteria to EumicrotiA. 



Includes Avicula costata, Morris & Lycett ; A. digitata, and 

 apparently Monotis interlaevigata, Quenstedt, and A. cifgnipes, 

 Phillips. Mainly, if not entirely, confined to the Jurassic rocks. 



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