62 



M. RUTA 



C D 



Fig. 5 Juliaecarpus milnerorum gen. et sp. nov. Late Ordovician. Upper Ashgill, Rawtheyan, Upper Ktaoua Formation, Morocco. Camera lucida sketches 

 of outline of suranal plate in different individuals. A, EE 3184, x 7.5. B, EE 3178, x 13. C, EE 31 19, x 13. D, EE 3121, x 7.5 (seen from the inside). 



griffei Ubaghs, 1969) or by a mosaic of relatively large, polygonal 

 elements (as in Reticulocarpos hanusi Jefferies & Prokop, 1972). 



Internal aspect of the thec a. The internal surfaces of both the 

 supracentralia and the infracentralia are featureless. The surface of 

 the marginalia facing towards the inside of the theca is trough-like 

 (Fig. 3; PI. 3, figs 1-5; PI. 4, figs 1^). Its cross-section does not show 

 abrupt changes in curvature, but it varies considerably in depth 

 depending upon the relative width of the dorso-lateral and ventral 

 projections of the marginalia. Thus, at the level of the antero-lateral 

 angles of the theca, the surface is approximately semiparabolic to 

 semicircular in cross-section, whereas halfway along the length of 



the lateral thecal margins, its section is semielliptical. It becomes 

 shallower and broadly hyperbolic at the level of the postero-lateral 

 angles of the theca. 



The internal surfaces of plates M', and M^ and of the zygal bar 

 show a complex morphology. In fully articulated specimens of 

 Juliaecarpus, the dorso-lateral projections of M'^ and M^ are 

 largely visible in dorsal view. They contribute laterally to the 

 medial parts of the antero-lateral angles of the theca and project 

 medially into the apophyses for the aulacophore insertion (see 

 above). M'^ and M, do not differ remarkably from each other 

 except for the presence of a posteriorly directed process contribut- 

 ing to the zygal bar in M' In what follows, therefore, I shall 



PLATE 5 



Juliaecarpus milnerorum gen. et sp. nov. Late Ordovician, Upper Ashgill, Rawtheyan, Upper Ktaoua Formation, Morocco. All latex casts coated with 

 ammonium chloride. 1, EE 31 15. x 10; laterally compressed and disrupted theca in dorsal aspect, with displaced supracentralia and poorly preserved 

 styloid and ossicles. 2, EE 3069, x 10; almost complete theca in dorsal aspect, with slightly displaced marginalia and supracentralia; note disrupted plates 

 of proximal aulacophore. 3, EE 307 1 , x 15; isolated proximal aulacophore plates, ossicles, cover plates and proximal-most portion of theca in dorsal 

 aspect. 4, EE 3098, x 10; poorly preserved marginalia and styloid articulated with first ossicle in left lateral view. 5, EE 3157, x 15; isolated plate M,in 

 dorsal aspect. 6, EE 3 1 5 1 , x 15; poorly preserved styloid with broken anterior spike in ventral aspect. 



