46 FOSSIL ECHINI OF THE WEST INDIES. 



to the peristomal border. The peristome is round, excentric, being 8 mm. 

 nearer to the anterior than to the posterior border of the test. Periproct 

 on the ventral side is situated 5 mm. from the posterior border of the test. 

 The tubercles are small, widely spaced on the dorsal side, somewhat larger 

 and more crowded on the ventral side. 



This species is known only from the holotype, which is a beautifully 

 preserved specimen. It measures 22 mm. in height, 108 mm. in length, 

 and 84 mm. in width across ambulacra II and IV, which is the widest 

 part of the test. The ambulacral petal III measures 40 mm. in length ; 

 petals I and V measure 37 mm. and petals II and IV measure 30 mm. 

 in length; they all measure 18 mm. in width at the widest part. 



Clypeaster platygaster is well characterized as a species by the excep- 

 tionally flat ventral surface, the nearly closed petals with very broad 

 poriferous areas, and the remarkable attenuated interporiferous areas. 

 Another marked distinction of the species is the deeply depressed 

 dorsal area surrounding the only slightly elevated central part of the 

 abactinal surface. 



This species bears considerable resemblance to C. oxybaphon, but 

 differs in the relative size and shape of the petals, and differs markedly 

 in that platygaster is perfectly flat ventrally, while oxybaphon is con- 

 cave. Clypeaster platygaster also resembles Laganum elongatum, but 

 in C. platygaster the petals are not sharply pointed distally, the porif- 

 erous areas are very much wider, and the test is flat ventrally. In 

 Laganum elongatum, on the other hand, the petals are sharply pointed 

 distally, the poriferous areas of the petals are narrow, and the test is 

 concave around the peristome. 



Oligocene, Havana, Cuba, not far from the university buildings; 

 the holotype and only known specimen, collected by Barnum Brown, 

 American Museum of Natural History, No. 18569. 



Family LAGANIDjE Desor, 1857. 

 Genus LAGANUM Gray, 1825. 



Type species. — Echinodiscus laganum Leske, 1778, Add. ad Klein, 

 p. 140. 



The genus Laganum among Recent species is an Indo-Pacific type 

 in its distribution, but fossil species have been referred to the genus 

 from Europe and North America as well as the Far East. It is inter- 

 esting that a West Indian fossil species has been described. The 

 resemblance of Laganum to Clypeaster is very marked, but the test in 

 Laganum is very flat, never highly arched. The petals are pointed at 

 the tips and the auricles are fused into one piece, whereas in Clypeaster 

 the test is more or less high and usually arched, the petals are rounded 

 at the tips, and the auricles which give attachment to lantern muscles 

 are separated, not fused. Laganum also closely resembles Peronella, 

 but Laganum has 5 genital pores, or in one Recent species 6 genital 



