182 SALENIA 



the disc is so intimately soldered to the test that it is sometimes difficult at first sight to 

 recognize its limits." A comparison of the English with the French specimens showed 

 them to be specifically identical, and thus M. Sorignet was the discoverer, but Eorbes the 

 namer, of this well defined species. 



c. — Species from the Upper White Chalk. 

 Salenia geometrica, Agassiz, 1838. PL XLIII, fig. 2 a — g, fig. 3 a, b. 



Salenia geometrica, Agassiz. Mongr. Echinodermes, pi. i, figs. 25 — 32, p. 1 1, 1838. 

 Cidaris ? vesiculosus, Portlock. Report on the Geology of Londonderry, pi. xviii, 



fig. 5, p. 358, 1843. 

 Salenia scutigera? Forbes. In Dixon's Geology of Sussex, pi. xxv, fig. 23, 1850. 



— Portlockii, Forbes. In Morris's Cat. of Brit. Foss., 2nd ed., p. 89, 1854. 



— — Woodward. Mem. of the Geol. Surv., Decade V, Append., 



p. 5, 1856. 



— geometrica, Cotteau et Triger. Echinides du Depart, de la Sarthe, pi. xlvi, 



figs. 1—7, 1860. 



— scutigera, Cotteau, pars. Paleontologie Francaise, Terrain Cretace, torn. 



vii, p. 154, pi. 1036, 1864. 



Diagnosis. — Test sub-globose, elevated, convex above, contracted and concave beneath ; 

 ambulacra narrow, slightly flexuous, marginal granules separated by two rows of granulets ; 

 inter-ambulacra wide, plates slightly radiate ; two rows of tubercles, seven to eight in each, 

 the ambital large, the basal small ; miliary zone with large sparse granules and minute 

 granulations ; apical disc moderate, of a regular geometrical figure, flattened, two thirds 

 the diameter of test; sutures punctuated; plates nearly equal in size; mouth-opening 

 small, one third the diameter of test. 



Dimensions. — a. Altitude, eight lines ; latitude, nine lines (Mr. Searles Wood's 

 specimen). 

 b. Altitude, eleven lines ; latitude, one inch (Mr. King's specimen). 



Description. — The species to which this Urchin has been referred is considered by 

 Professor Desor and M. Cotteau to be the Salenia scutigera, Gray ; as I am doubtful 

 about the identity of Dr. Gray's form, I have retained the name given by Professor 

 Agassiz, seeing that he has published good figures and a clear description of this species 

 in his beautiful Monograph on the Salenies. S. geometrica is the largest species of the 

 genus at present known. The test is elevated and sub-globose, slightly flattened at the 

 upper and under surfaces. The ambulacral areas are narrow and slightly flexed, with two 

 marginal rows of close-set granules, fourteen to sixteen in each, and separated by a 

 double row of minute granulation extending down the middle of the area (PL XLIII, 

 fig. 2 c,g,f). The poriferous zones are narrow and slightly flexed, the pores unigeminal 



