CLARK: THE CIDAKIDAE. 183 



TYLOCIDARIS. 



Tylocidaris Pomel, 1883, Class. Meth. Gen. Ech., p. 109. 

 Plato 1054, fiffs. 1-7, Pal. Franc. Terr. Cret., 7, Cotteau, 18G2. 



Test small or of moderate size, much as in Doroeidaris ; coronal plates 6-8 ; 

 areolae distinctly sunken, sometimes large, and tending to merge together vertically ; 

 primary tubercles large, smooth, and imperforate ; median interambulaeral and am- 

 bulacral areas and poriferous zones as in Cidaris or Doroeidaris ; pores large, close 

 together, slightly oblique. Abactinal system of moderate size, about .45-.60 h. d. 

 Actinostome somewhat smaller than abactinal system. Primary spines very stout, 

 club- or acorn-shaped. Secondaries and pedicellariae ? 



It is difficult to know how much weight can wisely be laid on the absence of 

 perforations in the tubercles, but it is a character never shown in perfect tubercles 

 of living Cidaridae. On the whole, the combination of imperforate tubercles with 

 the curious short, stout spines makes the genus easy to recognize. Doderlein 

 ('87) lists four species, all from the Cretaceous of Europe. 



CIDARIS. 



Cidaris Leske, 1778. Add. Nat. Disp. Ech., p. 17. 



Test moderately high ; vertical diameter usually about .60 h. d. (ranges from 

 .50-75) ; thick and solid (in metularia, thickness of an ambulacral plate at ambitus 

 is about .55 of its horizontal length) ; coronal plates 6-9 (sometimes 10, very rarely 

 11); areolae not sunken but tending to merge together actinally ; median inter- 

 ambulaeral area little or not at all sunken, more or less uniformly tuberculated ; 

 sutural lines often not visible at all ; ambulacra .20-.35 of interambulacra in width ; 

 poriferous zones little sunken ; median ambulacral area with a single conspicuous 

 marginal series of tubercles and 1-3 (rarely none, or in large specimens 4 or 5) 

 irregular vertical series of much smaller ones between ; sutural lines more or less 

 obscured and not conspicuously sunken ; pores oblique, with distance between two 

 of same pair about equal to diameter of a pore and with surface of interval more 

 or less elevated. Abactinal system .30-.50 h. d. Actinostome .40-.55 h. d., usually 

 larger than abactinal system, sometimes half as large again. Primary spines about 

 equal to h. d. (range from .65-1.60 h. d.), stout, cylindrical or terete, usually blunt, 

 slightly rough but not thorny, covered with longitudinal series of granules which 

 are usually low and rounded but may be conspicuous and sharp ; actinal primaries 

 not peculiar, little or not at all flattened ; ends rounded and generally fluted. 

 Secondary spines flat, truncate, rather broad and not tapering towards tip, which 

 may indeed be widened. Pedicellariae of 3 kinds present as a rule, but tridentate 

 may be wanting, or rarely large globiferous ones fail ; latter have curved valves, 

 large terminal opening, and no end-tooth. 



This genus is one of the most easily recognized of the family, although some of 

 the individuals with long spines approach quite nearly in appearance to Tretoci- 



