40 Revieus — Dr. Walcotf's Camhnan Paleontology. 



are indicated by an apparent! j' chalky deposit, their condition being 

 thus analogous to the sand-filled ampullae of some recent Spatangids. 



Among the minor points discussed are the traces of the coelomic 

 epithelium in Echinoconm, the rudimentary perignathic girdle in 

 Ananchjtes, and the notable differences, chiefly in the disposition of 

 tlie pores, between the inside and the outside of the ambulacra of 

 Echinoconus. Furthermore, the growth-bands in Spatangus purpiireus 

 and Micraster cor-anguinum are shown to be similar. Dr. Klinghardt's 

 examination of specimens of Ananchytes from the Danian of Malmo 

 and the Senonian of England has enabled him to determine that 

 changes have taken place in their internal organization at different 

 horizons as well as in the shape-variations familiar to chalk-workers. 

 The positions of the gut-line and of the water-vascular system in 

 particular show these changes. Another interesting fact is brought 

 forward, viz., that one finds in specimens from the 3Iarsupites-zont' 

 a slight swelling of the ambulacral plates in the direction of the inter- 

 ambulacra. As a result of this, the water-vascular system comes to 

 lie in a kind of channel : the fine peristomial structure has in 

 consequence gradually shi-unk, and has disappeared altogether in 

 examples from Malmo. The important conclusion derived from 

 a detailed comparison between Spatangus purpureus and Micraster 

 is that Spatangus recapitulates the Micraster-stage in its ontogeny. 



In addition to the purely palajontological details. Dr. Klinghardt 

 has furnished many observations of great geological interest. At 

 Newhaven he noted a deposit in process of formation that he considers 

 to explain the origin of echinoderm breccias. This was a silt, rich in 

 broken echinoderm tests, that had accumulated in a sheltered creek, 

 but owing to the incursions of rough seas had come to be intercalated 

 with coarse - textured bands containing a different fauna. The 

 enormous preponderance of small urchins in some marine beds is 

 shown to be due to the fact that the larger species of which fragments 

 are found had swallowed them together with sea-sand. The Kewhaven 

 and the Petersberg (Maestriehtian) echinoderm breccias are proved to 

 have been formed under preciselj" similar conditions. 



Dr. Klinghardt attributes the preservation in flint of the form of 



the internal organs of fossil sea-urchins to rapid infilling of their 



tests, due to sudde^i precipitation of silica. In support of this opinion 



he instances the uniformity of the thickness and sharp definition of 



the tabular flint bands to be found at certain horizons in the English 



Chalk. The paper concludes with observations on the oecology of 



living echinoderms ; and reasons are assigned for regarding the 



variations in the facies of Ananchytes and Micraster as attributable to 



differences in nature of habitats. n -n r< 



C. P. Chatwin. 



IV. — Cambeian Geology and Pal^iontology. No. 6 : Olebellvs 

 AND OTHER Geneea OF THE Mesonacid^. Smith souiau Miscellaneous 

 Collections, vol. liii, 1910. 



SINCE the publication of the memoir on the Olenellus fauna in 

 1891, Dr. C. D. "Walcott has made a hu'ge collection of these 

 primitive forms from the Lower Cambrian rocks of the United States, 



