ISG COTTALDIA. 



Affinities and Differences. — This magnificent Salenia in point of size resembles S. 

 fieometrica, var. Portlockii, ft-om the White Chalk. The test, however, is more elevated, 

 the apical disc thicker and more prominent, and the inter-ambulacral areas resemble each 

 other in the number and development of the tubercles in each rovi' ; the oblong vent and 

 oblong mouth-opening are, however, special to S. magnifica. 



Locality and StratigrapJiical Position. — This Urchin was collected from the Upper 

 Chalk near Norwich, and belongs to the British Museum collection. 



Genus — Cottaldia, Desor, 1856. 



Echinus, pars, Z^CBn!>, 1820; Mimster, 1826; Forbes, 1849. Arbacia, Gray, 1835. 



Cottaldia, Desor, 1856. 



Test small, sub-globular, sides inflated, more or less depressed at the poles. 

 Shell lobed, divided into fifteen sections ; the five most prominent form the ambulacral, 

 and the ten others, grouped in pairs, the inter-ambulacral areas. Poriferous zones 

 narrow, straight ; pores unigeminal. Tubercles small, mammillated, imperforated, 

 uncrenulated, very numerous, homogeneous, and forming on each plate a close-set hori- 

 zontal row. Granules microscopic, placed on all the inter-tubercular spaces. Apical 

 disc solid, narrow, forming a prominent ring, composed of five perforated, rhomboidal, 

 ovarial plates, and five cordate oculars ; all the elements of the disc are covered with close- 

 set granules. Mouth -opening moderate, lodged in a concave depression of the base ; peri- 

 stome sub-pentagonal, decagonal, and feebly notched. 



The genus Cottaldia forms a very natural group of small fossil Urchins appertaining 

 to the Cretaceous and Tertiary formations ; well characterised by their sub-globular form, 

 and the abundance and uniformity of their tubercles, arranged in horizontal series 

 over the entire test. Much confusion formerly existed between Arbacia, Gray ; Echino- 

 ciDARis, Desmoulins ; Poltcyphus, Agassiz ; and Magnosia, Michelin. This, however, 

 has been in a great measure removed by clearer definitions of the genera retained, the 

 suppression of those that were doubtful, and the establishment of the genus Cottaldia. 



The uniformity of the tubercles, Prof. Desor remarks, attains its maximum in this 

 small genus; and this character accords with its peristome, which is narrow and depressed, 

 and its pores, which are unigeminal throughout the zones. These characters distinguish 

 Cottaldia from the neighbouring types with which it has been confounded up to the 

 present time. It is dedicated by M. Desor in honour of his friend M. Cotteau, the 

 learned author of the ' Echinides fossiles de 1' Yonne,' and of the ' Paleontologie Fran^aise.' 



