304 PROCEEDINGS OF THE ACADEMY OF [1889. 



geographically, and a few have also a very considerable geologic 

 range. A number of the now recognized species will probably prove 

 to be identical with forms previously known, but these cannot be, 

 with certainty, determined except by a direct comparison of the 

 type specimens. The synonymy, however, of a portion of the 

 Macrochili lias been made out as indicated beyond. 



As already suggested the forms of this group appear to be easily 

 separable into two sections: the first typified by Macrochilus acutum 

 (Sowerby) and Soleniscus typieus Meek and Worthen; and the 

 second having for its typical representative Macrochilus ponderosum 

 Swallow. The shells of the first group are characterized by being 

 more or less elongate or fusiform, with the spire elevated, acute; 

 body whorl forming about half the length of the shell ; aperture 

 subelliptic, or oval, acutely angular posteriorly; columella im- 

 perforate, provided with a conspicuous revolving fold or ridge, 

 which, however, in the perfect specimen is often scarcely descernible 

 exteriorly, but as it passes inward becomes more and more pronounced 

 and is oftpn accompanied by a second, though much less prominent, 

 fold of similar character; test thick. 



The columellar ridge is in most examples usually hidden more or 

 less completely by the imbedding matrix filling the aperture. By 

 the removal of the outer lip the twisted fold becomes more apparent. 

 In a perfect specimen of Soleniscus newberryi (Stevens) this ridge is 

 scarcely defined at the aperture, but towards the interior of the 

 shell it gradually assumes greater prominence, becoming very much 

 elevated, very sharp, and bordered on each side by a broad rounded 

 canal, the outer of which is narrower and considerably deeper than 

 the other. On the inner margin of the second furrow there is often 

 developed an obtuse prominence much less conspicuous than the first 

 and best defined a short distance from the apertural margin. From 

 this point it soon becomes obsolete inwardly and finally disappears 

 altogether. In the majority of the forms referred to Soleniscus the 

 fold on the columella presents essentially the same characters, and 

 is generally well disclosed by breaking away the outer lip of the 

 shell slightly. When the exterior wall of the last whorl is entirely 

 removed the interior features of the columella are still better 

 exhibited and for a much greater distance. 



As generally recognized the Macrochilus group has a wide range 

 in time, beginning, according to the species described, in the 

 Silurian and continuing to the present time. Some of the forms 



