DUBLIN VkTVnXL UI8T0XT SOCnSTT. ^8 



ON THX 0ENT7S EUOMPUALUS, AND ITS RELATIONS TO PLEUBOTOMARIA AND 

 THE HALIOTID^. WITH TWO PLATES. BY REV. PROFESSOR HAUOHTON. 



( Vide page 26.) 



The Palaeozoic genus Euomphalus is one that has given much trouble to 

 palaeontologists, in consequence of their hesitation to give the same names 

 to genera of the secondary and Palaeozoic periods, and also in conse- 

 quence of serious variations in the different fossils that have been called 

 by this name. Thus, it would be very difficult to state in what essen- 

 tial particulars the Euomphalus of Sowcrby differs from the Straparolus 

 of Montfort, and both from the common Solarium of Lamarck. M. 

 D'Orbigny characterizes Solarium by its quadrangular or rounded 

 month, the umbilic mostly crenulated on the rim; and Straparolus 

 by its round or square spines, not crenulated on the rim of the umbilic. 

 M. Pictet justly observes that this crenulation of the rim of the umbilic 

 is not a constant character in Solarium, being, in fact, almost peculiar 

 to the Tertiary species ; while in the Cretaceous epoch there are only 

 two or three species with the rim of the umbilic crenulated. I may add 

 to this, that the well-known Evsmphalm pugilis has the crenulation of 

 the umbilical mai'gin as fully developed as any fossil or recent So- 

 larium. 



Mr. Phillips founds the genus Euomphalus on the character that in the 

 old shells the upper portion of the shell is partitioned off by the animal, 

 which was provided with the means of depositing a septum of shell oc- 

 casionally, after the manner of the chambered Cephalopoda. There 

 was no communication, however, kept up between the chambers and the 

 body of the animal, as in the Cephalopoda. This character, however, is 

 far from being well established as a general characteristic of the Euom- 

 phalus, having been only established in some of the species, as JE, 

 pentangulatusy E, acutus, and E.pugilis. M. de Koninck maintains that 

 all the species of Euomphalus have the external lip slit, like Pleuroto- 

 maria, — a circumstance which, if true, would undoubtedly require us to 

 remove them from the family of the Trochidae into that of the Halio- 

 tidae. The chai-acter noticed by M. De Koninck is found in some of our 

 Irish Carboniferous species, and is beautifully exhibited in a specimen, 

 E. regina (Haughton) found by me at Sheffield, Queen's County. This 

 specimen would be referred at once to E. acutttSy were it not for the 

 accidental preservation of a portion of the shell and of its original co- 

 louring and markings, which show that it had a deep slit in the exterior 

 lip, and a sinus band, not distinguishable from that of many species of 

 Pleurotomaria. 



While the Euomphalus thus approaches Pleurotomaria in some of 

 its forms, it connects itself with Hadiotis in the remarkable species ge- 

 nerally assigned at present to Cirrus (not Sowerby). There are three 

 species of this kind known in the Palaeozoic period : — C eristatua of Ire- 

 land, (7. Goldfussi of the Eifel, and C. armatm of Belgium. These fossils 

 have the form of Euomphalus, and are provided i^ith a series of aper- 



L 



