323 



" Surface markings not at all well preserved in either of the specimens 

 collected, but apparently consisting of fine concentric lines of growth. 

 Hinge dentition and muscular impressions unknown. 



" Approximate dimensions of the specimen figured : maximum length, 

 fifteen millimetres ; greatest height, eleven mm. ; maximum width, or 

 thickness through the closed valves, nearly nine mm. 



" Trenton limestone, Ottawa, E. Billings : four nearly perfect but badly 

 preserved specimens. 



" J/, hrevis can be distinguished at a glance from M. tener, M. rugosa and 

 M. recta, by its comparatively short, tumid and regularly convex valves." 



Sptroceras Beauportense, Whiteaves. (Nom. nov.) 

 Plate 33, figs. 2 and 2 a. 

 Orthoceras Beauportense, Whiteaves 1898. Ottawa Naturalist, vol. XII, p. 11?. 



" Shell rather below the medium size, longicone, straight and tapering 

 so gradually that the few specimens which the writer has seen are almost 

 cylindrical. Surface marked by low, rounded, narrow transverse annula- 

 tions, with numerous minute and close-set, transverse thread-like raised 

 lines between and upon them, all of which are crossed by small and narrow 

 but comparatively distant longitudinal ribs or ridges. The transverse 

 annulations average from two and a half to three millimetres apart, at 

 their summits, and are separated by shallow depressions nearly twice as 

 wide as themselves. The longitudinal ribs or ridges are equidistant, 

 uniform in size, and, on an average, about one millimetre and a half 

 apart. The crossing of these ribs by the transverse annulations makes a 

 very rogular and rectangular reticulation, which is plainly visible to the 

 naked eye, but the crowded transverse raised lines cannot be well seen 

 without the aid of a lens. Internal structure and shape and relative 

 position of the siphuncle unknown. 



" Trenton limestone at Parent's quarry, Beauport, near Quebec City, 

 D. N. St. Cyr, 1888 : one well preserved testiferous specimen not quite 

 two inches in length and with a considerable portion of its surface buried 

 in the matrix. A similar specimen, but with fche whole of the outer sur- 

 face visible, from the same locality, has been lent to the writer by the 

 authorities of LaA al University. 



" This fiuely sculptured shell seems to be closely allied to the 0. pseudo- 

 calamiteum (Quenstedt) Barrande,"* which 'Hya.tt says ia a, Bawsonoceras, 

 " but it wants the intermediate longitudinal ridges characteristic of that 

 species." It apparently belongs to Barrande's ' Group 6 ' of the genus 



* Systeme Silurien de la Boheme, tome II, texte 3, 1874, p. 261, pi. 217, fig. 8 ; pi. 

 222, figs. 11 and 12 ; pi. 228 ; pi. 236, figs. 11-16 ; et pi. 361, figs. 1517. 

 6 



