188 DESCRIPTION OF [Polygastrica. 



found either solitary or in pairs. Size l-570th to 1 -280th. 

 Found with the preceding ; also fossil in flints. 



176. XANTHIDIUM /wrc^^m. The forked Xanthidium 

 has a globular green spinous lorica, and occurs either 

 singly or in pairs, or at most four are connected together. 

 A figure with a large glandular body within each is shown 

 at fig. 110, which will convey to the reader the best idea 

 of their form. According to Ehrenberg, some of these 

 animalcules possess only one forked spine, the others 

 being short and broad. Size l-5?0th to -1- 280th. The 

 spines are usually half the length of the body. 



177- XANTHIDIUM? ramosum. . The branched Xanthi- 

 dium has a globose lorica, covered with spines, trifid or 

 branched at their extremities. The number of spines 

 varies from six to twenty. They are found either single 

 or in pairs. They are not figured by Dr. E. In plate xii., 

 Mr. Bauer has drawn them at fig. 511 and 515. This 

 species is only known in a fossil state ; it occurs in the 

 flints of most chalk formations. Dr. Ehrenberg thinks 

 its true place is the genus Peridinium, as traces of a 

 transverse groove have been observed. Size 1-1 150th to 

 l-280th. 



178. XANTHIDIUM ? difforme is shewn at^. Ill, which 

 represents a pair of these highly magnified ; they have 

 a turgid lorica, of a green colour. Found with Micras- 

 terias. Fossil specimens are shewn in plate xii., fig. 513 

 and 5 14. Size l-430th. 



179. XANTHIDIUM crassipes. The thick blunt-spined 

 Xanthidium has a globose lorica, larger than the other 

 species. There are two varieties : in one the thick blunt 

 spines appear distinct ; in the other, they often appear 



