26 CIDARIS. 



The second type. — Tubercles with the summits of the bosses more or less crenulated, 

 are found in the Triassic and Oolitic rocks. 



There are some exceptions to these rules, for Cidaris marginata, Goldfuss, and 

 Cidaris laevigata, Desor, both from the Coral Crag, have smooth bosses ; and some 

 species from the Neocomian and Cretaceous strata are said to have the summits of 

 these eminences crenulated. 



A. Cidaris from the Lias. 



Cidaris Edwardsii, Wright. PI. I, fig. 1 a, b, c, d, e,f. 



Cidaris Edwardsii, Wright. Annals and Magazine of Natural History, 2d series, vol. xiii, 



p. lGl.pl. 11, fig. 1 a—f. 



Test crushed ; the true form therefore unknown. Ambulacral areas narrow, gently 

 flexed, and furnished with two rows of small perforated marginal tubercles, and a median 

 row of smaller tubercles irregularly interspersed amongst them ; the marginal tubercles 

 being alternately larger and smaller ; poriferous zones wide, with large, closely approximated, 

 oblong pores ; inter-ambulacral areas about four times the width of the ambulacral, with 

 two rows of large primary tubercles, the areolas of which are confluent throughout ; miliary 

 zones wide, and covered with numerous small granules ; primary spines long, showing a 

 complex structure ; secondary spines short, with blunt apices ; the surface of both covered 

 with delicate longitudinal lines ; mouth armed with five powerful jaws, each having carinated 

 ridges on their convex surface ; upper part of the test unknown. 



Description. — The great argillaceous deposits of the Oolitic group — the Lias, the 

 Oxford Clay, and the Kimmeridge Clay — were formed under conditions which appear to 

 have been unfavorable to the development of Urchin life ; for, although these rocks have 

 been industriously explored, they have hitherto yielded very few remains belonging to the 

 Echinoidea : this remark does not apply only to the English Oolitic group, but is appli- 

 cable to the whole series as developed on the continent of Europe. Although a few forms 

 of Cidarida lived in the Silurian, Devonian, Carboniferous, Permian, and Triassic 

 seas, still it was in the Jurassic ocean that they existed in any considerable numbers ; and 

 this fact gives increased interest to the study of the anatomy of these Oolitic representatives 

 of this most beautiful family, one of the oldest of which we have figured in PI. I, fig. 1. 

 It is much to be regretted that the specimen before us is the only one of the species that 

 has been found in Gloucestershire in anything like a state of preservation, a few fragments 

 of its test having been rarely collected in two or three other localities. At Lyme Regis one 



