SYNOPSIS OF THE MOLLUSCA OF THE 

 CRETACEOUS FORMATION, 



Including the Geographical and Stratigraphical Range and Synonymy, 

 BY WILLIAM M. GABB. 



MARCH, 1861. 



PREFACE. 



IN September 1859, I published in the Proceedings of the Aca- 

 demy of Natural Sciences of Philadelphia, a u Catalogue of the In- 

 vertebrate Fossils of the United States." Having, since that time, 

 been repeatedly requested to prepare a supplement, with the additions 

 that have been made to the subject, and such corrections as I may 

 have found necessary, I have preferred going over the whole of the 

 formation, bringing it up to the year 1860, since the latest work of 

 the kind only extends to 1850. 



My former catalogue was at first prepared for my own use only and 

 afterwards published at the advice of some of my friends. Not be- 

 ing intended originally for general use, and having been compiled 

 during a press of other engagements, it was necessarily imperfect in 

 many particulars. In the present paper I have endeavored to remedy 

 these defects. Having access, in the collection of the Academy, to 

 all the known types of Dr. Morton's, and a large number of Mr. 

 Conrad's species, I am happily able to settle some points which have 

 long been in doubt. Thus, the original specimens from which Dr. 

 Morton described the species, Inoceramus Barabini, I find belong, as 

 has long been suspected, to two very distinct species : one is probably 

 I. prollematicus, Schlt. ; the other will have to retain the name /. 

 Barabini. The types of Clypeaster geometricus, and C. florealiSj 

 both very badly figured in the " Synopsis," and with scarcely a gene- 

 ric description, still exist in the collection. The first is probably, as 

 Agassiz, in his Catalogue Raisonne considered it, a Pygurus, although 

 being but an imperfect cast, there is yet some uncertainty. The 

 latter is not a Favjasia as considered by d'Orbigny and 

 is a true Catsidnlns. 



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