THECIDIUM. 



TESTA inaequivalvis, subirregularis, subaequi- 

 latera, externa valvse eoneavse parte affixa; 

 imperforata. Valva infera processibus duobus 

 cardinalibus, internis, brevibus, et area irre^- 

 gulariter subtrigona ad umbonem acutiusculum 

 extensa. Valva altera planiuscula, basi extern^ 

 appendicula brevi, obtusa ; interne processibus 

 duobus lateralibus cardinalibus, et lamellis 

 configuratione varia. Ligamentum nullum. 



Separated with great judgment from Terebratula^ by 

 M. De France^ being attached by the outside of the shelly 

 while the Terebratulae, as we have shown in a former 

 number, are fixed by a fibrous substance passing through 

 the aperture at or near the point of the umbo. We have 

 corrected the generic name from Thecidea to Thecidium^ 

 at the recommendation of our learned friend the Rev. Dr, 

 Goodall. 



Shell inequivalve, rather irregular, nearly equila- 

 teral, attached by the outer part of the concave valve; 

 ifnperforate. Lower valve with two internal, short, car- 

 dinal processes, and an external, rather irregularly 

 triangular area extended to the umbo, which is somewhat 

 acute. Upper valve rather flat, with a small, short, ob- 

 tuse appendage at its base externally, and two small 

 lateral cardinal processes within, and variously curved 

 laminae always attached to the inner disk of the shell. 

 Hinge without any ligament, but the valves cannot be 

 separated without some portions of the lateral processes 

 heing broken : in which respect it resembles the greater 

 number of the Brachiopoda, 



Of the recent species of this Genus, the configuration 

 of whose internal laminae is so singular, we are at pre- 



