Oligopygus

&lt;h3&gt;About:&lt;/h3&gt;

&lt;p&gt;The Eocene sea urchin &lt;i&gt;&lt;b&gt;Oligopygus&lt;/b&gt;&lt;/i&gt; has a medium-sized test and is found throughout the south-eastern part of North America, the Caribbean, the West Indies, and Central America. &lt;/p&gt;

&lt;h3&gt;Identifiable features:&lt;/h3&gt;

&lt;p&gt; &lt;/p&gt;
 * Test of medium size, elongate to subcircular in outline; margin and adoral surface rounded, sunken towards peristome
 * Apical system subcentral, monobasal, with four gonopores. Sexual dimorphism in size of genital pores (larger in females)
 * Petals well developed, open distally, anterior petal III longest, posterior pair (V & I) shortest. Pores strongly conjugate, equal number of pores in pores series in the same petal. Ambulacra beyond petals composed of primary plates, demiplates, and in some species included plates; demiplates and included plates small, thin, not reaching interior of test, absent near peristome
 * Peristome subcentral, opening subpentagonal to subtrigonal, in deep transverse depression or trough
 * Periproct inframarginal, midway between peristome and posterior margin
 * Buccal pores present on edge of peristome
 * Tubercles small, irregularly arranged both adorally and adapically

&lt;h3&gt;Species and locations:&lt;/h3&gt;

&lt;p&gt; &lt;/p&gt;
 * O. costuliformis Jeannet, 1928; Late Eocene, Trinidad
 * O. curasavica Molengraaff, 1929; Upper Eocene, Curacao
 * O. haldemani (Conrad, 1850); Late Eocene, Florida
 * O. jamaicensis Arnold & Clark, 1927; Middle Eocene, Jamaica
 * O. kugleri Jeannet, 1928; Late Eocene, Trinidad
 * O. nancei Cooke, 1941; Late Eocene, Venezuela
 * O. phelani Kier, 1967; Late Eocene, Florida, USA
 * O. pinguis Palmer in Sanchez Roig, 1949: Middle-Late Eocene, Cuba
 * O. putnami Israelsky; 1933; Upper Eocene, Mexico
 * O. rotundus Cooke, 1942; Late Eocene, Alabama, USA
 * O. sanchezi Lambert, 1932; Middle Eocene, Cuba
 * O. wetherbyi de Loriol, 1888; Late Eocene, Florida, USA
 * O. zyndeli Jeannet, 1928; Late Eocene, Trinidad

Sources: http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/taxa/taxon.jsp?id=727