3G8 PALEONTOLOGY OF ILLINOIS. 



more or less thickened, and generally twisted into an obtuse 

 fold below. 



As originally proposed by Phillips, this genus was made to include, in addi- 

 tion to the typical forms, species belonging apparently to our genus Solcniscus, 

 and to Naticopsis of McCoy. If we were to follow the rule adopted by some, 

 of always regarding the first species described by an author, under a new generic 

 name, as the type of the genus, we would have to take Buccinum breve, of 

 Sowerby, as the type of Macrocheilus, that being the first species described by 

 Phillips. And as that shell seems to be a nodose species of McCoy's subse- 

 quently proposed genus Naticopsis, we would probably have to substitute the 

 name Macrocheilus for the Naticopsis group. As Phillips, however, only re- 

 ferred the B. breve provisionally to his genus, and distinctly states that he 

 thought it allied to Natica, and the species B. arculatum and B. imbricatum to 

 his genus Loxonema, while he says he regards the other species as "alone suffi- 

 ciently peculiar to deserve a generic title," it is evident he did not view any of 

 those just mentioned as typical examples of his new genus. Consequently we 

 must look for the type amongst the other included species, which are Buccinum 

 acutum, Sowerby, and Macroclieilus elongatus and 31. harpula, Phillips.* Hence 

 de Koninck, and others who first followed Phillips in the use of this generic 

 name, have regarded 31. acutus and other congeneric species as typical forms; 

 which conclusion has been adopted generally amongst Palaeontologists. Con- 

 sequently in proposing the clearly distinct genus Soleniscus (probably including 

 31. elongatus of Phillips), we adopted the generally accepted opinion in regard 

 to the particular group for which the name Macrocheilus should be retained, as 

 had also been done by McCoy in proposing his genus Naticopsis. 



As thus understood, Phillips's genus includes those rather thick, smooth, 

 subglobose, oval, or more or less fusiform shells, with convex whorls, an oval 

 aperture, neither distinctly notched nor provided with a canal below, and a 

 more or less callous inner lip, usually twisted into an obtuse revolving fold on 

 the imperforate, somewhat flattened columella, such as 31. acutus, Sowerby (sp.), 

 M. primigenius, Conrad (sp.) .31. maculatus, de Koninck, M. ventricosus, Hall, 

 M. Newberyi, Stevens, etc. These shells vary considerably in the elevation of 

 the spire, though it is always acute at the immediate apex, even when depressed. 

 In texture, smoothness of surface, the thickening and often obtusely folded 

 character of their inner lip, as well as in general appearance, they remind one 

 of those ponderous Cretaceous and Jurassic shells often referred to Actseonella; 

 such for instance as A. Reynauxiana, d'Orbigny, A. obtusa and A. clliptica, 

 Zekeli, upon which one of the writers has proposed to found a distinct genus, 



* He also included M. ? neglectus, Phillips ; but as he did so with a query, we could 

 not view it as one of the intended typical species. 



