LEPIDESTHIDAE. 393 



figures the relative size, angles, and position of pores of ambulacral plates are seen. The adam- 

 bulacral plates on the interior are much wider than on the exterior. The other interambulacral 

 plates are narrower and lower on the interior than on the exterior, due to the smaller space 

 occupied on the interior by thick plates in a curved test. 



Family LEPIDESTHIDAE Jackson. 



Lcpidoccntridac (pars) Loveii, 1874, p. 39; (pars) Jackson, 1896, p. 241; (pars) Klein, 1904, p. 16. 



Palaeechinidac (pars) Loven, 1874, p. 40. 



Archaeocidaridac (pars) Loven, IS74, p. 42; (pars) Duncan, 1889a, p. 8; (pars) Zittel, 1879, p. 485. 



Melonitidac (pars) Zittel, 1879, p. 484; (pars) Duncan, 1889a, p. 15. 



Lepidesthidae Jackson, 1896, pp. 206, 241; Tornquist, 1897, pp. 730, 734; Gregory, 1900, p. 304; Klem, 



1904, p. 22; Lambert and Thiery. 1910, p. 123. 

 Hybochinidae Tornquist, 1897, pp. 732, 734. 

 Rliocchinidae (pars) Lambert and Thiery. 1910, p. 121. 



This family is enlarged from what it was as I first published it, to include certain old genera 

 and one new one. It presents a wide range of characters, yet is fairly homogeneous as a whole. 

 As a family it is related to the Palaeechinidae, from which it is distinguished essentially by the 

 fact that the plates are imbricate. Test spheroidal, elliptical, obovate, or flattened. Ambula- 

 cra are narrow or wide, with, in each area at the mid-zone, from two to twenty columns of plates 

 which imbricate weakly or strongly adorally, and laterally bevel under the adambulacral plates. 

 As in the two lowest genera of the Palaeechinidae, the lowest genera of this familj' (Lepidechi- 

 nus, Perischodomus) have only two columns of plates in an ambulacral area, but other genera 

 have from four columns upward. Pore-pairs are in peripodia, situated nearest the next adjacent 

 interambulacrum or exceptionally (Pholidocidaris) near the middle of each plate. The am- 

 bulacra ventrally and dorsally (as in the Palaeechinidae) are simpler than at the mid-zone, 

 when that area is complex. Ambulacral plates bear secondary tubercles and spines only, 

 or (Meekechinus) small primary with secondary tubercles. In the character of the number of 

 ambulacral columns, this faniilj' includes the most specialized of Palaeozoic Echini. 



The interambulacra are wide or narrow with from three to thirteen columns of plates at 

 the mid-zone in each area. The plates are thick or thin, and imbricate aborally and from the 

 center laterally and over the ambulacrals on the adradial sutures. This last is an important 

 point, as in the Palaeechinidae, in which imbrication is lacking, interambulacral plates bevel 

 under (not over) the ambulacrals. Ventrally, apparently always in this family (Plate G4, 

 fig. 2), the primordial interambulacral plates are in the basicoronal row, there being, as far 

 as known, no resorption of the base of the corona. From the basicoronal row passing 

 dorsallj', there are two plates in the second row and three in the third, dorsal to which additional 

 columns, if developed, come in as in other Palaeozoic types. Interambulacral plates bear sec- 

 ondary tubercles and spines only, or primary with secondary tubercles and spines. 



