606 DESCEIPTXON OF [Poli/gastrtca. 



Concerning these peculiar, yet distinct organisms, almost nothing 

 is known, save their external configuration. 



DicTYOCHA aculeata. — Cells in the form of a ring, each cell spiny on 

 its inner aspect. External spines long, but unequal in length, and 

 radiating from the circumference. Fossil in the chalk marl of Oran, 

 Caltanisetta, Zante, and Greece ; alive in the waters of the Cattegat, 

 near Tjorn. Diameter of fossil forms 1 -2304th to 1-11 50th; of 

 living, 1- 1440th to 1-11 50th, without reckoning the horns. 



D. Fibula. — Form concave, rhomboid or 

 square, with four spiny angles externally, 

 and four interspaces. Fossil in chalk marl, 

 Oran, Caltanisetta, &c. Alive in sea-water 

 near Christiana. Locomotion not observed. 

 Diameter 1-1 150th to 1 -560th. 



D. Speculum. — In form of a ring, spines six, 

 long, but unequal in size, radiating from the circumference, cells 

 not spiny within, six open spaces surround a central one. Fossil in 

 chalk marl of Caltanisetta, Oran, and Greece. Alive in the Baltic. 

 Contains, when living, green granules, and locomotion is perceptible 

 after long observation. Diameter l-860th (P. 15, fig. 62 a front 

 view ; fig. 63 a side view (living.) 



D. Crux. — Cells five, combined in a quadrate form around a central 

 foramen; angles spinous. Diameter 1 -624th. Fossil in chalk marl 

 of Caltanisetta, Sicily. 



D. heptacanthis. — CeUs thirteen, in an heptagonal form ; seven of 

 the cells marginal ; each of the seven angles furnished with radi- 

 ating spines. Diameter 1 -552nd. Fossil in Greek marl. 



D. Nmicula. — Cells eight, figure oblong, obtuse, cylindrical, reti- 

 cidar, with a median septum like a Navicula. Fossil in chalk marl. 



D. polyaetis. — Unarmed, with nine rays, ten marginal cells, and 

 one central, arranged in a reticulate stellate form. In chalk marl. 



D. (?) splendens. — Oblong, tabular, with dentate apertures (cells) 

 thirteen in number. If it be calcareous, it is similar to Coniopelta. 



D. trifenestra. — Quadiilateral, with elongated aculeate b 



angles, and three internal dentate cells. St. Domingo. 'C^-^ 



