THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE V. VOL. VIII. 



No. VIII. — AUGUST, 1911. 



OT^IGKEIDT^IIL AETICLES. 



I. — Sedgwick Museum Notes. 



A New Fossil from Girvan. 



By F. E. Cowpee Eeed, M.A., F.G.S. 



(PLATE XV.) 



Helminthochiton thraivensis, sp. nov. (Plate XV.) 



Description. Body elongated, narrow, composed of a longitudinal 

 series of eight imbricating plates, and marginal girdle (?) of spicules. 



First or head-plate transversely subcircular, broader than long, 

 smallest of the series ; about two-thirds the length of second plate ; 

 surface gently convex, very weakly carinated in posterior median part ; 

 posterior edge arched back, slightly angulated and projecting ; inferior 

 surface with submarginal concentric thickening. 



Second to seventh plates of nearly equal size and shape, trans- 

 versely trapezoidal in outline, about twice as wide as long, bent down 

 strongly on each side of median axial line at angle of about 90° ; 

 imbricating backwards in middle. Anterior margin broadly emarginate, 

 being excavated by shallow rounded median sinus ; lateral portions 

 of anterior margin arched forward as rounded lobes, with outer 

 (=inferior) angle broadly rounded and passing into inferior margin, 

 which is nearly straight and parallel to axial line. Posterior margin 

 angulated in middle line, projecting backwards as bluntly pointed 

 broad lobe slightly overlapping succeeding plate behind. Posterior 

 and inferior margins meet at obtuse angles, or in seventh plate at right 

 angles. Surface of plates in middle portion of body marked by pair of 

 faint shallow depressions diverging anteriorly and broadening to 

 anterior outer angles. Middle portion of plates internally thickened 

 in a transverse direction, so as to make internal casts somewhat saddle- 

 shaped. Posterior margin of plates furnished internally with narrow 

 thickening close to edge, with several much finer parallel linear 

 thickenings behind it. Upper surface of second to seventh plates 

 ornamented with two (or sometimes more) strong regular concentric 

 strise parallel to anterior and outer edges of plates, one being situated 

 usually at about one-fourth the length and the other at one-half the 

 length, with finer concentric striaa between them. 



Eighth or terminal plate smaller, less strongly bent along middle, 

 gently convex, semi-elliptical in shape, rounded behind, with sub- 

 marginal concentric thickening around anterior and outer edges on 

 inferior surface. 



decade v. — vol. vrn. — no. vrn. 22 



