AMPYX INCURVUS. 161 



Genus AMPYX, Dalman. 

 Ampyx incurvus, sp. nov. Plate XX, figs. (3—8. 

 1903. Ampyx mammillatus, Sars (?), Reed, supra, p. 22, pi. iii, fig. 13. 



Some better preserved specimens of the species referred to Ampyx mammillatus 

 (Sars) ? from the Balclatchie Group occur amongst the new material which 

 Mrs. Gray has collected from Dow Hill and Ardmillan. From these head-shields 

 it is found that the glabella is strongly elevated in front above the cheeks, sloping 

 up to the frontal spine gradually from the neck, but very abruptly from the 

 anterior margin of the shield, beyond which it slightly projects. The pairs of 

 lateral pits and oblique furrows on each side of the glabella generally unite, so as 

 to enclose one pair of longitudinally oval areas, as in A. hastatus, Ruedemann. 1 The 

 carinatiou of the glabella is more marked than was indicated in fig. 13, PI. III. 

 The spine which is situated at the pointed anterior end and highest part of the 

 glabella is not directed straight forwards, but curves gently upwards and then 

 backwards, attaining a length equal to more than twice that of the glabella. 

 The lateral furrows or pits on the glabella are usually more strongly marked than 

 indicated in the specimen previously figured. 



The curvature of the peculiar rostral spine, as well as the shape of the glabella 

 and its oval lateral impressions, recalls A. (Lonchodomas) hastatus, Ruedemann, 

 from the Trenton Conglomerate of Rysedorph Hill, N. Y., but the carinatiou in the 

 latter is more marked and the lateral furrows on it are dissimilar, while the rostral 

 spine in our form is rounded and not prismatic. The specific name incurvus is sug- 

 gested, as it is undoubtedly distinct from A. mammillatus and other allied species. 



In one specimen there are six thoracic segments attached to the head-shield in 

 position. The axis is subcylindrical, tapering very slightly towards the pygidium, 

 and it is four fifths the width of the pleural portions on each side. Each axial ring 

 is furnished with a pair of strong, Avell-defined, rounded lateral nodes. The 

 horizontally extended pleurae possess the usual characters of the genus, but the 

 furrow is distinctly diagonal near the axis and widens outwards towards the 

 extremity of the pleura. 



1 Ruedeuiaun, 'Bull. 49, New York State Mus.' (1901), p. -48, pi. iii, figs. 1—10, 30. 



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