182 SILURIAN MOLLUSCA. 



Belleropkon suhdecussatus (M^Coy). 



Sp. Char. Globose, of one and a half or two very rapidly en- 

 larging whorls, subcompressed towards the very obtusely an- 

 gular or rounded circumference ; sides gibbous ; umbilicus 

 small, deep, partially exposing the whorls ; diameter 4|^ lines ; 

 in proportion to diameter, width -f^-^, length of mouth j-^q, 

 diameter of umbilicus -i-^q', surface with strong transverse 

 ridges arching backward from the umbilicus to the undefined 

 band, forming a wide V-shaped sinus ; about four or five of 

 these transverse ridges in the space of 1 line near the mouth ; 

 they are crossed by much finer spiral striae, about the same 

 distance apart, from one to three of which are usually stronger 

 than the rest near the band. 



This species is extremely like the carboniferous B. decussatus 

 (Flem.), but has the transverse strise much stronger than the 

 spiral ones. 



Rare in the schists of Llanrwst and fine sandstone of Mulock, 

 Dalquorhan, Ayrshire. 



{Col. University of Cambridge.) 



Holopella (M'Coy), n. g. 



Gen. Char. Shell spiral, elongate, slender, of numerous gra- 

 dually increasing whorls, generally crossed by slightly arched 

 strise; mouth circular, with the peritreme entire ; base rounded, 

 with or without a minute umbilicus. 



These shells have hitherto been confounded with the recent 

 genus Turritella, from which they differ completely in the entire 

 peritreme and definite round margin to the mouth, thus approach- 

 ing much nearer to Scalaria. From Chemnitzia they differ in 

 the smaller size of the body-whorl, and in neither it nor the 

 mouth being produced anteally. 



Holopella gracilior (M'Coy). 



Bp. Char. Very slender, spiral angle 15°, whorls smooth (num- 

 ber unknown), slightly and evenly convex, suture deep, simple, 

 sutural angle 95° ; width at base 5 lines, length of last whorl 

 3 lines. 

 This is distinguished from the H. ohsoleta by its more slender 



spire (as indicated by the difference in their spiral angles), less 



convex whorls, &c. 



Schists of Dinas Bran, Llangollen. 

 [Col. University of Cambridge.) 



Holopella intermedia (M'Coy). 

 I provisionally give this name to a species agreeing exactly, 



