Vol. 58. ] REFERRED TO MURCHISONIA AND PLEUROTOMARIA, 5515) 
— 
of the upper part of the body-whorl; moreover, the angularity below 
the band on the body-whorl is less pronounced, and the lines of 
erowth, though varying in strength, are not lamellar and they do not 
recede and advance so strongly asrepresented in the figures of L. tenwi- 
striata. This species evidently belongs to the Perangulata subsection 
of the Perangulata section of Ulrich. 
Dimensions.—The crushed specimen figured in Pl. IX, fig. 9 
consists of eight whorls in a length of 155 millimetres. That figured 
in Pl. IX, fig. 7, has about six whorls, measuring 13°5 mm. in length, 
and 8 mm. in width; the length of the sinus in its outer lip, if entire, 
would be about 4°5 mm., and would thus equal about one-fifth of 
the circumference of the last whorl. 
Locality and Horizon.—Balclatchie (Ayrshire), in rocks of 
Llandeilo age [ Lapworth]. 
Family PLEUROTOMARIID &, d’Orbigny. 
Genus Pleurotomaria, Defrance. 
Subgenus PatmoscHisMA, nov. 
Diagnosis.—Shell depressed-conical. Whorls few in number, 
flattened or slightly concave above, base convex. Band situated on 
the widest part of the whorl, near the middle of the body-whorl, 
low down on the earlier whorls, appearing just above the suture ; 
lower margin coinciding with the periphery, concave, bounded on 
each side by a strong raised thread. Outer lip retreating with a 
moderate degree of obliquity above, oblique immediately below the 
band, and then forming a convex curve. Slit short, with parallel 
edges, about one-fifth the circumference of the body-whorl in 
length. Aperture probably subquadrate, but imperfectly known. 
Type, Paleoschisma gurvanense, sp. nov. 
Remarks and Resemblances.—The characteristics of this 
subgenus do not exactly agree with those of any previously 
described genera or subgenera of the Pleurotomariide. It comes 
nearest to Hotomaria, Ulrich' in general form, and in possessing a 
concave band, bounded on each side by a strong thread situated on 
the apical side of the whorl; but it differs in having a distinct 
though short slit, instead of a sinus in the outer lip. The form 
of the slit greatly resembles that of Trepospira spherulata® (Conrad), 
which species is figured by Ulrich as the type of his genus Trrepo- 
spira, Paleoschisma is, however, distinguished in the band being 
visible above, instead of hidden by the suture on the earlier whorls, 
and in the absence of ornamenting nodes. It differs from Schizo- 
lopha,* the only Ordovician genus described by Ulrich with a slit 
in the outer lip, in the form of the shell and in the character and 
position of the band, this latter in Schizolopha being prominent 
1 Final Rep. Geol. & Nat, Hist. Surv. Minnesota, vol. iii, pt. 11 (1897) p. 954, 
2 Ibid. pp. 957 & 1081. 3 Ibid. p. 952. 
