GASTROPODA. I"-"- 1 



OphlUttna.) 



the upper side of the whorl*, the band, in low-spired pleurotoraarians, being almost 

 inv.m.iMy situated on the periphery. Again, the rounded character of the whorls 

 of the interior casts, which m-'-f-Mtated a strong deposit of shell beneath the 

 external keels, the lower especially, recalls a common condition among species of 

 Ophilrt'i. l-'.wnnplmtus and I'leuronoiua, but not of any of the Pleurotomariidct. 



According to our view, Hisingeria is a strongly marked descendant of the 

 // <otomi or Opliilet't type. Though the general aspect is widely different, the real 

 differences are not so great as they appear on first sight, and, what is more important, 

 they are rather easily accounted for. In Hishujfrin the slit-band or keel has been 

 reduced in prominence and moved inward from the outer edge of the upper side of 

 the whorl to near the suture line, while the revolving stria-, which as a rule are but 

 ill developed in llelicotoma, have been strengthened and the outer basal angle 

 somewhat extravagantly thickened. The last feature is perhaps the most striking 

 peculiarity when compared with, for instance, llelicotoma planulata Salter, but in our 

 //. <uli'futiilr<itn the outer basal angle is somewhat prominent, while in our //. 

 margmata, a new species from the extreme top of the Lower Silurian, a similar 

 feature is even more abruptly developed. Still, we doubt very much that the latter 

 is in any wise an ancestor of Hisingeria planorbis, the real line of descent from 

 Ofthileta being, in our opinion, as yet undiscovered or unrecognized as such. 



Eccyliopterus, Itemele, which we place in this family, has already been discussed 

 in connection with Raphistoma on pages 935 to 933. The genus is a good one and 

 includes shells with contiguous whorls similar in most respects to those of Ifelico- 

 loma, and others in which they are more or less completely disconnected. The 

 latter have usually been confounded with Eccyliomphalut, but as we have endeavored 

 to show, the true position of the genus is nearer Ophiletn and llelicotoma than 



liomphalus. The distinguishing character of Eccyliopterus lies in the remarkable 

 development of the upper keel which projects beyond the surface of the whorls like 

 a high collar. 



Genus OPHILETINA, n. gen. 



! >! remarks on this genus see page 1"> 



Only two or possibly three small species of this interesting genus are known. 

 In these the whorls are rather slender, contiguous or partly free, coiled almost in 

 the same plane, and either hexagonal or subquadrate in section. On the upper side 

 and forming the outer edge there is a sharply elevated convex or flat-topped ridge 

 which looks very much like a true slit-band, being covered with strongly recurved 

 lines (lunulu.*) and terminating anteriorly in a well-marked notch. On the vertical 

 outer side the lines of growth are bowed forward in the middle, on the lower side 



