PANAMIC DEEP SEA ECHINI. 



DESMOSTICHA Haeckel. 



CIDARIDJE Mtiller. 



In describing the shape of the test of the Cidaridae, certain points of 

 general interest are brought out from the comparison of different stages 

 of growth. 



If we place the odd anterior ambulacrum forward, the pentagon formed 

 by the abactinal system will have its odd face forward, Fig. 1, while that 



of the anal system will have 

 its odd side toward the poste- 

 rior extremity. With the pen- 

 tagons of the actinal system 

 and of the teeth the opposite 

 is the case, Fig. 2. The out- 

 line of the test may similarly 

 be pentagonal with the odd 

 face either anterior or posterior. When the odd face is posterior, the inter- 

 ambulacral areas do not bulge out as they do when the odd face is anterior. 

 Figs. 1, 2. Intermediate conditions will give the test a more or less circu- 

 lar equatorial outline, as in Dorocidaris pa7iamensis, Fig. 3 ; Centrocidaris 

 Doederleini and Porocidaris Cobosi, Fig. 4, have an anterior odd pentagonal 

 face, and P. Milleri, Fig. 6, an odd posterior face. 



Fig. 1. 



Fift. 2. 



30 mm. 



Fig. 3. Dorocidabis panamensis. 



Porocidaris Cobosi 



