22 FOSSIL ECHINI OF THE WEST INDIES. 



Cotteau's figure of the larger specimen he has restored the outlines 

 so as not to show the lateral crushing. The larger crushed test measures 

 15 mm. in height, 17.5 mm. across the plane of crushing, and 26 mm. 

 in the plane of crushing at the mid-zone (plate 1, fig. 12). The width 

 of an ambulacrum at the mid-zone is 3.5 mm. and of an interam- 

 bulacrum is 9 mm. Eight ambulacral plates abut against an inter- 

 ambulacral plate at the mid-zone. In this specimen there are 6 

 interambulacral plates in a column in each area. As noted in the 

 description, Cotteau says that the periproct is a little larger than the 

 peristome, but as far as one can judge in their somewhat crushed 

 condition, it appears that they are practically of the same size. In 

 the smaller specimen, which is not crushed at all, the periproct and 

 peristome are of the same size. This matter of similar size of periproct 

 and peristome is a good character to distinguish mel/itensis from the 

 nearly allied C. tribuloides, in which the peristome is larger than the 

 apical disk. The smaller test is better preserved, not being compressed. 

 It measures 9 mm. in height and 17 mm. in diameter; width of ambu- 

 lacrum 2.5 mm., of interambulacrum 7 mm. The diameters of the 

 periproct and peristome measure about 8 mm. each. In this smaller 

 specimen there are either 5 or 6 plates in each interambulacral column, 

 in some columns the sixth plate not yet having appeared, whereas 

 the larger specimen had 6 plates in each column. The youngest plates 

 dorsally bear tubercles, but they have not yet developed perforations, 

 this being the typical character of young plates dorsally in Cidaris. 

 The spines measure up to 20.5 mm. in length and 3 mm. in diameter 

 at the widest part. 



In addition to the above, there are in the U. S. National Museum 

 3 fragmentary tests in the Guppy collection which probably were not 

 collected by Cleve or studied by Cotteau. They have 5 or 6 plates 

 in each interambulacral column, and one of them shows apophyses of 

 the perignathic girdle for the attachment of lantern muscles. 



Cidaris melitensis is closely allied to C. tribuloides, but is at once 

 distinguished by its much more sparsely tuberculated coronal plates 

 and wider ambulacra ; also by the fact that in melitensis the peristome 

 and apical disk are practically of the same diameter, whereas in tribu- 

 loides the peristome is much wider than the apical disk. 



Oligocene, Anguilla formation, island of Anguilla, Guppy collection 

 ex Cleve, 2 tests and 3 spines, evidently the originals of Cotteau's 

 plate 1, figs. 1-10, U. S. Nat. Mus. No. 115399. Anguilla, Guppy 

 collection, 3 fragmentary tests, U. S. Nat. Mus. No. 115412. Miocene, 

 a single fragmentary spine, evidently referable to this species from 

 (loc. 11) Mayo Village Quarry, Trinidad, F. W. Penny collector, 

 U. S. Geol. Sur. station 8583. Miocene, 2 small spines 12 and 14 mm. 

 long respectively, apparently attributable to this species, are from 

 the Gurabo formation, Rio Mao, one-half mile above ford at Cercado 



