74 



M. RUTA 



M'5 



B 



Fig. 9 Reticulocarpos hanusi Jefferies & Prokop. Middle Ordovician, 

 Llanvim, Sarka Formation, Czech Republic. Schematic reconstruction of 

 external aspect. A, dorsal view. B, ventral view (redrawn and modified 

 after Jefferies & Prokop, 1972 and Cripps & Daley, 1994). 



of Juliaecarpus show their maximum degree of curvature at the 

 level of plates M', and M„ whereas in Reticulocarpos, such 

 margins are more strongly convex at the level of M^ and M^, on the 

 right side of the theca, and of M', and M',, on its left side. In 

 addition, the dorso-lateral projections of the marginalia of 

 Juliaecarpus are slightly to much wider than their ventral projec- 

 tions, whereas in Reticulocarpos, the difference in width between 

 the two kinds of projections is much smaller. 



2. Unlike Reticulocarpos, Juliaecarpus possesses a large suranal 

 plate. This plate is probably not unique to Juliaecarpus, as I shall 

 explain below, because an enlarged plate occupying the posterior 

 part of the dorsal integument seems to have been present also in 

 Beryllia and Domfrontia (see discussion of these genera below). 



3. In Juliaecarpus, plates M'^ and M^ do not send medial projections 

 forming a dorsal bar as in Reticulocarpos. In the stylophoran 

 phylogeny presented by Parsley (1997, 1998), the presence of a 

 dorsal bar characterizes a clade uniting Reticulocarpos, 

 Prokopicystis and Hanusia, contrary to the hypotheses of rela- 

 tionships presented by Cripps ( 1991 ) and Cripps & Daley (1994) 

 (but see also Daley, 1992). 



4. Plates M', and M, of Juliaecarpus are less strongly convex 

 laterally than their namesakes in Reticulocarpos and their dorso- 

 lateral projections are slightly wider than those of more posterior 

 marginalia. The dorso-lateral projections of M', and M, contrib- 

 ute only in part to the antero-lateral angles of the theca, whereas 

 in some other ankyroids (but not in Reticulocarpos), these 

 marginalia send more strongly developed medial branches form- 

 ing most of the antero-lateral angles of the theca. 



5. The length of the posterior process of M', in Juliaecarpus is 

 almost twice the length of the posterior zygal plate; such a 

 process is also slightly wider than the ventral projections of the 

 marginalia throughout its length and its posterior end lies slightly 



posterior to the suture between M, and M^ and slightly anterior 

 to that between M', and M'^. In Reticulocarpos, on the other 

 hand, the M'| process is comparatively shorter and stouter than 

 that of Juliaecarpus and its posterior half is less wide than the 

 ventral projections of the marginalia; furthermore, its posterior 

 end lies anterior to both the M^/M^ and the M',/M'j sutures. In 

 addition, the posterior zygal plate of Reticulocarpos probably 

 did not contact the thecal frame (see discussion below). 



6. The lateral margins of M, and M', in Juliaecarpus carry shallow 

 denticulations, as opposed to the pronounced, saw-like serra- 

 tions present along the lateral margins of M„ M\, M, and M', in 

 Reticulocarpos. 



1 . Plates M'^ and M^ of Juliaecarpus, assuming their correct iden- 

 tification, are comparatively much smaller than their namesakes 

 in Reticulocarpos and much narrower than more anterior 

 marginalia. In Reticulocarpos, these plates also differ in shape 

 and size, whereas in Juliaecarpus, they are almost mirror images 

 of each other. 



8. In Juliaecarpus, the transition from the retiform stereom texture 

 on the median part of the dorso-lateral projections of the 

 marginalia to the striated texture on the peripheral flange is more 

 gradual than in Reticulocarpos and no cancellose or irregular 

 stereom is interposed between these two kinds of textures. 



9. The peripheral flange oi Juliaecarpus is less developed than that 

 of Reticulocarpos and appears to have possessed comparatively 

 shallower lateral fringes and less irregular trabeculae; in addi- 

 tion, it seems to have been confined mainly to the anterior half of 

 the lateral margins of the thecal frame. 



10. Some of the supracentralia of Juliaecarpus, especially those on 

 the anterior half of the dorsal integument, approach a bilaterally 

 symmetrical arrangement and it is always possible to distinguish 

 some larger plates in a central position flanked by longitudinal 

 rows of smaller plates comprised between the marginal frame 

 and the oro-anal axis. Conversely, the supracentralia of 

 Reticulocarpos are not arranged according to a particular pat- 

 tern. 



11. The spike-like processes on the styloid and ossicles of 

 Juliaecarpus are comparatively less high, less recurved and 

 more laterally flattened than those of Reticulocarpos and pointed 

 almost exactly downward rather than downward and rearward in 

 life. The stereom texture of the styloid and ossicles is slightly 

 more compact and consists of comparatively smaller perfora- 

 tions in Juliaecarpus than in Reticulocarpos. 



The internal aspect of the theca permits more limited comparisons 

 between Juliaecarpus and Reticulocarpos. At the level of the zygal 

 bar, the most obvious difference between these two genera is the fact 

 that in Juliaecarpus, the ridge on the dorsal surface of the zygal 

 process of M'^ does not extend as far forward as in Reticulocarpos, in 

 which such a ridge reaches the suture between M^ and M'^. The 

 preservation of the internal side of Mj and M'^ in Juliaecarpus is not 

 as detailed as in Reticulocarpos. A comparison between the recon- 

 struction of these plates in Juliaecarpus and the reconstruction 

 provided by Jefferies & Prokop ( 1 972) for Reticulocarpos highlights 

 major differences in the morphology of this region of the theca in the 

 two ankyroids. 



Two other stylophorans, Beryllia miranda and Domfrontia 

 pissotensis, both from the Llandeilo of France, reveal interesting 

 similarities with Juliaecarpus. As in Juliaecarpus, some of the 

 supracentralia of both Beryllia and Domfrontia, especially those 

 aligned along the oro-anal axis, are slightly to much larger than the 

 remaining supracentralia. In the case of Beryllia, the supracentralia 

 which occupy the anterior third of the dorsal integument are 



