A NEW STYLOPHORAN ECHINODERM 



75 



M'3 



M'4 



M'4 



B 



Fig. 10 Beryllia iniranda Cripps & Daley. Middle Ordovician, Llandeilo. 

 Pissot Formation, France. Schematic reconstruction of external aspect. 

 A, dorsal view. B, ventral view (redrawn and modified after Cripps & 

 Daley, 1994). 



arranged in broadly transverse rows (e.g. Cripps & Daley, 1994: 

 pi. 2, fig. 5). 



In the reconstruction of Beryllia provided by Cripps & Daley 

 (1994), the thecal frame shows four left and four right marginal 

 plates (M'j and M^ are presumably absent) (Fig. 10). In the same 

 reconstruction, a subpentagonal and an irregularly parallelogram- 

 like plate of subequal size appear along the posterior margin of the 

 dorsal integument and roof over the obliquely oriented anal opening. 



However, at least one of the specimens of Beryllia figured by 

 Cripps & Daley ( 1994: pi. 2, fig. 5) shows a transversely expanded, 

 subrectangular supracentral plate between the posterior ends of M'^ 

 and Mj. The plate in question carries an irregular fringe along its 

 posterior margin and the average size of its stereom mesh pores is 

 slightly larger than that of other dorsal integument plates. It may be 

 homologous with the suranal plate of J uliae carpus but its outline and 

 relative position with respect to the surrounding plates are poorly 

 defined. 



The following skeletal features distinguish Juliaecarpus from 

 Beryllia: 



1. Higher thecal length/width ratio. Based on the measurements 

 provided by Cripps & Daley (1994), Beryllia shows a thecal 

 length/width ratio of about 1 :2, as opposed to the ratio value of 

 1 :72 reported in Juliaecarpus. 



2. Smaller length difference between the left and the right lateral 

 thecal margins, accompanied by more bilaterally symmetrical 

 thecal outline and less oblique position of the anal opening. In 

 Beryllia, the theca is slightly asymmetrical, due to length differ- 

 ence between the left and the right marginalia. Such difference 

 characterizes all comute-like ankyroids and indicates that the 

 process of symmetrization of the thecal outline must have pre- 

 ceded the acquisition of paired marginalia of equal (or subequal) 

 shape and size. Juliaecarpus exemplifies a stage of this process, 

 in that the presence of an almost bilaterally symmetrical theca is 

 accompanied by almost complete symmetrization of the more 

 posterior pairs of marginalia, whereas the anterior marginalia 



(especially M', and M,) are still markedly different (see also 

 comparison with Nanocarpus below). 



3. Less pronounced convexity of lateral thecal margins (see also 

 point 2 above). 



4. Lesser elongation of 1VI3 with respect to other marginalia (see 

 also point 1 above). 



5. Dorso-lateral projections of marginalia wider than their ventral 

 projections (see also point 1 in the comparison with 

 Reticulacarpos). 



6. Greater difference in shape and size between the ventral projec- 

 tions of M| and M,. The ventral projections of these marginalia 

 appear to be subequal in Beryllia, but markedly different in 

 Juliaecarpus). 



1. Much smaller difference in length between M', and M, (see also 

 point 2 above). 



8. Slenderer, straighter and comparatively more elongate zygal 

 process of M', (see also discussion of this structure below). 



9. Less clear demarcation between M' ^ and its zygal process. While 

 in Beryllia the posterior zygal process of M'| widens abruptly in 

 its anterior part to become confluent with this plate, in 

 Juliaecarpus the boundary between M'| and its process is less 

 clearly evident (see description of the internal surface of this 

 plate above). 



10. Adoral plates longer than wide and separated by a leftward 

 concave suture. The occurrence of a median adoral in Beryllia is 

 possible, based on the poor material figured by Cripps & Daley 

 ( 1 994). The left and right adoralia of Beryllia are wider than long 

 and, in comparison with those of Juliaecarpus, they are much 

 smaller than the dorso-lateral projections of M'^ and M|. 



11. Apparently larger number of broad, polygonal, more regularly 

 arranged plates on the anterior third of the ventral integument. In 

 Beryllia, only a few large polygonal supracentralia in a subcentral 

 position are visible. These are flanked by irregularly shaped 

 plates, apparently more numerous on the left than on the right. As 

 pointed out in the anatomical description above, the supracentralia 

 of Juliaecarpus form transverse rows of elements arranged in a 

 bilaterally symmetrical (or nearly so) pattern on the anterior half 

 of the dorsal integument (see also point 1 1 in the comparison 

 with Reticulacarpos). 



12. Strongly developed, recurved, spike-like styloid and ossicular 

 processes. The styloid and ossicles of Beryllia possess low, 

 poorly pronounced keel-shaped longitudinal processes, clearly 

 different from the conical processes of Juliaecarpus (see also 

 point 1 1 in the comparison with Reliculocarpos). 



The material of DomfroiUia is less well preserved than that of 

 Beryllia, but it does permit limited comparisons with Juliaecarpus. 

 As in the case of Juliaecarpus and Beryllia. it is difficult to ascertain 

 the precise number of lateral marginal plates, due to the poor 

 preservation of the rearmost ends of the thecal frame (Fig. 1 1 ). 



The inside of what I interpret as a possible suranal plate is partly 

 visible in the holotype of Domfrontia (Cripps & Daley, 1994: pi. 1, 

 fig. 5). The right part of such a plate, assuming its correct identifica- 

 tion, is hidden by one of the rearmost preserved infracentralia. The 

 visible portion of it shows a more regular outline than the suranal of 

 Juliaecarpus, a less extensive posterior fringe attached to an appar- 

 ently semielliptical posterior margin and an almost straight, thickened 

 anterior margin. However, unlike the suranal of Juliaecarpus and. 

 perhaps, Beryllia, the like-named plate of Domfrontia does not seem 

 to show a remarkably different stereom texture with respect to other 

 integument plates. 



I'he most important morphological differences when Domfrontia 

 is compared with Beryllia and Juliaecarpus are as follows: 



