1542 



THE VOYAGE OF H.M.S. CHALLENGER. 



Synopsis of the Orders and Families of PH^EODARIA continued. 



III. Order 



PILEOGKOMIA 



Skeleton a simple lattice- 

 shell, not bivalved, con- 

 stantly provided with 

 a peculiar large shell- 

 mouth placed on the 

 oral pole of the main 

 axis ; peristome usually 

 surrounded by peculiar 

 feet or teeth. (Shell 

 either spherical or ovate, 

 or of another form). 

 Central capsule excentrie, 

 placed in the aboral half 

 of the shell-cavity. 



IV. Order 



PH^EOCONCHIA. 



Skeleton a bivalved lattice- 

 shell, composed of a dorsal 

 and a ventral valve which 

 are completely separated 

 (rarely connected by a 

 ligament on the aboral 

 pole). Central capsule 

 enclosed bet ween the two 

 valves. 



Structure of the shell not 

 porcellanous (without 

 needles imbedded in a - 



punctulate 

 stance). 



cement^sub- 



Structure of the shell por- 

 cellanous, with peculiar 

 fine needles imbedded in 

 a punctulate cement- 

 substance (a circle of 

 pores around the base 

 of each radial tube). 



Structure of the shell 

 diatomaceous, with very 

 delicate and regular hexa- 

 gonal pores. No articu- 

 late feet, 



Structure of the shell alveo- 

 lar, with hollow alveoles 

 between a double plate. 

 A corona of articulated 

 feet around the mouth, . 



Structure of the shell of sim- 

 ple lattice-work, neither 

 diatomaceous nor alveo- 

 lar. No articulate feet, 



Surface of the shell pan- 

 elled or dimpled (spheri- 

 cal or polyhedral). Peris- 

 tome flat, 



Surface of the shell smooth, 

 even (ovate or subspheri- 

 cal). Peristome pro- 

 minent, 



The two valves of the bivalved shell thick and firm, 

 regularly latticed, without a galea or cupola on their 

 apex, and without hollow tubes, 



The two valves of the 

 bivalved shell very thin 

 and fragile, scarcely lat- 

 ticed, each with a conical 

 cupola or a helmet- " 

 shaped galea on its 

 sagittal pole or apex, 

 and with hollow tubes. 



Galea without rhinocanna 

 or nasal tube, without 

 frenula, . 



Galea with a rhinocanna or 

 nasal tube, both con- 

 nected by an odd or 

 paired frenulum, 



8. CHALLBNGEKIDA. 



9. MEDUSETTIDA. 



10. CASTANELLIDA. 



11. CIRCOPORIDA. 



12. TUSCARORIDA. 



13. CONCHAKIDA. 



14. CCEIXJDENDRIDA. 



15. CCELOGRAPHIDA. 



Order I. PREOCYSTINA, Haeckel (1879). 



Definition. PH^ODARIA without lattice-shell, either without any skeleton, or with 

 an incomplete skeleton, composed of numerous single pieces, which are scattered in the 

 calymma without connection. Central capsule placed in the centre of the spherical 

 calymma. 



