4G 
CRETACEOUS ECniNODER:MATA 
Ortuopsis smiLis, StoUczka. PI, VII, Eig. 2. 
Or. testa snhpentagone rotundata, depresso-hemispheriea, infra fere plana ; 
tiiherciilis primariis amhulacrallhus el inlerambulacralihiis tmerialibus, primis circa 
18-20 in qnaqne ordine, area intermedia gramilis niimerosis imtrncta, alteris 
paulo niajoribiis, nndecim in nna serie, abbreviate conoideis, mammellis parvis, 
depressis, spaciose perforatis ; qtiaque tabula interambnlacrali tubcrculo secundario 
majore ad angulum internum super iorem et altero paxdo minore ad angidum exteriorem 
site instructa, tub. ambobus brevissime niammillatis atque perforatis, stiperfeie reliqua 
gramilis nmnerosis incequalibus notata, granulo in angido externo inferiore site maxima 
sed non perforata ; zonis qioriferis modice angustis, poris bigeminatis circiter 66 in nna 
serie ; apertura rotundate decagona, lata, tertiam partem diamelri superante ; tabidis 
apicalibus indistincte granulosis; or if do anali irregulariter tetragona, angulis 
snbi'otmidatis prccdilo. 
T'liis is a Avell marked species of the rare gemts Orlhopsis, and although very 
closely allied to the Cenomanicn Orth, gramdaris,* (Ag. and Des.), this last is readily 
distinguishable hy the smaller number of granules on both the ambulacral and 
intei-amhulacral plates ; the latter are also distinctly higher in proportion to their 
length. 
Orth, similis has a nearly round shell, hut as the ambulacra, in spite of their tuber- 
cles being a little smaller than those of the interamhulacra, slightlj^ project beyond the 
periphery of the latter, there is at least an approach to pentagonal shape ; the upper 
side is depressedly hemispherical, the lower nearly flat, and the height exceeds half 
the diameter of the shell hy one millimeter. There are 56 regular pairs of pores 
in one zone ; only toAvards the aperture there is a very slight irregularity observ- 
able in position. On the ambulacra are eighteen to twenty tubercles in one row, on 
the interamhulacra only eleven. Each of the latter plates has, however, two unequal 
mammillated and perforated secondary tubercles in each of the upper angles, one 
large granule in the lower outer corner, and the rest of the surface round the 
groove-like areola is rather numerously unequally granular, at least considerably 
more so than in O. gramdaris. 
The apical plates are indistinctly granular, as in the latter species, and do not 
offer any peculiarity, but the anal opening is more irregularly quadrangular. The 
mouth is rather lai’ge, its Avidth being about two-fifths of the total diameter. 
Locality . — North of Chokouadapooram ; two specimens in an impure, sandy, 
reddish or pinkish limestone. 
Formation . — Arrialoor group. 
* Cotteau, Pal. Fran?, teir. cret., vii, p. 554, pi. 1130. 
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