180 Dr. T. Wright on Fossil Echinoderms 



alluded to. The tubercles on the basal portions of the anterior 

 and posterior interambulacra are not very large, but are disposed 

 with great regularity ; those on the ridge-like prominence of the 

 single interambulacrum are arranged in lines which radiate in 

 all directions from a point ; those on the pairs gradually decrease 

 in size from the mouth to the border ; between these two groups 

 of tubercles there is on each side a smooth track, corresponding 

 with the course of the postero-lateral ambulacra from the border 

 to the mouth : the anus is large and circular, and occupies the 

 upper part of the posterior border ; the subanal fasciole is de- 

 nuded ; the mouth is likewise large and transversely oval, and is 

 situated near the anteal sulcus. The apical disc is excentral, 

 being situated about the anterior part of the middle third of the 

 test ; it is small, and is perforated with four genital holes. The 

 superficial layer of the calcareous plates, which carries all the 

 fine sculpture of the test, is almost entirely denuded from the 

 dorsal surface ; one or two fragments alone remain to show that 

 the tuberculation was minute and close-set. 



Affinities and differences. — This species is distinguished from 

 S. Hoffmanni by the excessive elevation of the posterior part of 

 the test ; by the shorter, wider and more oval form of the peta- 

 loid ambulacra ; by the poriferous zones of the anterior pair 

 being more complete ; by the large dorsal tubercles being smaller 

 and fewer in number ; by having a less impressed anteal sulcus ; 

 a convex base, with smaller tubercles ; a ridge-like projection, 

 with a regular tuberculation of the basal portion of the inter- 

 ambulacrum, with smooth naked ambulacral tracks on each side 

 thereof. From S. Desmarestii it is distinguished by its short, 

 broad, petaloidal ambulacra, which are long and attenuated in 

 S. Desmarestii ; by the greater size, number and regularity of 

 the large dorsal tubercles, which are few, small and scattered in 

 S. Desmarestii ; the posterior region is not at all elevated in S. 

 Desmarestii, and the anus is transversely oblong, whilst in S. 

 De Koninckii the posterior part is much elevated, and the anal 

 opening is round. 



S. Desmarestii has a few groups of large tubercles on the 

 upper part of the single interambulacrum, which are entirely 

 absent both in >S. Hoffmanni and S. De Koninckii. The basal 

 region is so much covered up with matrix in the specimen of S. 

 Desmarestii before us, that we cannot institute a comparison 

 between this portion of its test and that of S. De Koninckii. 



Locality and stratigraphical range. — The two or three speci- 

 mens we have seen in the Earl Ducie's cabinet were collected 

 from the clay bed No. 2 at ]\Ialta ; they have all a deep ferru- 

 ginous colour, and are not well preserved. We dedicate this 

 species to our friend Dr. De Koninck of Liege, the learned 



