D)\ F. A. Bather — Eocene Echinoids from SoJcofo. 299" 



the type-locality, Havre, show normal heteronomy. It is desirable 

 that the genotype of Lintlda also should be examined on this point. 

 Till that has been done, we must be content to follow the diagnoses 

 of Duncan in this respect also. 



On the preceding interpretation of the genera, the specimens from 

 Garadimi belong to Semiaster. While the peripetalous fascicle 

 of A is visible quite clearly in places, the most minute and prolonged 

 scrutiny has failed to reveal any trace of a lateral fasciole. Con- 

 sidering, however, that its absence might just conceivably be due 

 to the weathering of the specimens, I investigated the structure 

 of the actinal surface, with the result that in B there was traced 

 normal heteronomy of interradius 1. Among the Tamaske specimens, 

 several show the lateral fasciole passing beneath the periproct, and 

 would therefore be referred to Linthia by most palaeontologists. 

 But they all have distinct normal heteronomy (PI. XI, Fig. 12). 

 Therefore I place them in Hemiaster. At the same time I have 

 thought it advisable, for the reasons given above, to compare them 

 with species of Linthia as well as of Hemiaster {Tracliy aster). 

 Finding nothing under either name with which they could be 

 placed, I venture to refer them to 



Semiaster sudanensis, n.sp. (PL XI, Figs. 6-13.) 



Diagnosis. — Ethmolysian, with 4 gonopores (= Trachjaster). 

 Outline elongate subovoid, with slight posterior truncation and deep 

 anterior sulcus. Length 100 ; ^ greatest width, at level of apical 

 system, which is eccentric in front, from 95 in young to 87 in adult ; 

 greatest height, at about 65 from anterior margin, from 63"7 to 

 71-8, average 68*6. Posterior truncation slopes upwards and 

 inwards, so that periproct is visible from above. Posterior interradius 

 subcarinate above, inflated on actinal surface. Margins of actinal 

 surface rounded, so that ambitus is at one-quarter the height above 

 base-plane. Summit depressed. Anterior ambulacral groove increases 

 in depth towards margin and continues to peristome. Paired 

 ambulacra increase in depth to one-third their length from apex, 

 and then decrease to almost flush at ends of petals ; II and IV 

 subtend 110°, length of petals about 53 to 45, adult number of 

 pore-pairs in series 26-28 ; I and V subtend 60°, length of petals 

 about 32 to 39, adult number of pore-pairs in series 19-21. Pores 

 conjugate, mostly elongate, outer twice length of inner. A line of 

 miliaries on the intervening ridges. Peristome depressed anteriorly, 

 with a projecting labrum. Periproct broadly lanceolate, more pointed 

 above. Primary tubercles crowded on dorsal surface, larger on actinal 

 surface, intermingled with secondaries on ambulacra I and V ; bosses 

 finely crenulate ; scrobicular areas depressed, with circle of miliaries 

 on abactinal surface, but with an inner raised rim on actinal surface. 

 Miliaries closely set on all intervening space. 



Description of the specimens. — A (B.M. registered E 4826) 

 is well preserved, with some adherent hard marly matrix ; the test, 



1 See footnote, p. 293. Length here = 21-32-3 mm. 



