206 HippuRiTiD-a;. 



and the teeth and apophyses so firmly wedged into their respec- 

 tive cavities as to suggest the notion tliat the valves had become 

 fixed about a quarter of an inch apart, and ceased to open and 

 close at the will of the animal. 



BiRADiOLiTES, d'Orbigny, 1850. Ligamental groove visible in 

 one or both valves, sometimes occupying the crest of a ridge, 

 and bordered by two similar areas. Fossil, 5 sp. Chalk ; 

 France. B. canaliculatus (cxviii, 38). 



LAPEiROUSiA, Bayle. B. Jouanetti, Desm. 



SYNDONiTES, Piroua, 1869. Cardinal teeth grown together 

 almost in their entire length. B. Stoppaniana, Pir. Cret. ; Friaul. 



SPH^RULITES, de la Merthe, 1805. (Acardo, Brug. lodamia, 

 Defrance. Birostrites, Lam. Dipilidia and Agria, Math. 

 Heterocaprina, Munier-Chalmas.) Attached valve generallj^ 

 elongately conical with longitudinal, more or less foliated surface 

 and the margins radiately ribbed, internally with a single umbonal 

 rib extending the whole length of the valve. Free valve smaller, 

 similar in form and structure to that of Radiolites, but with a 

 median tooth or columella corresponding to the hinge-rib of the 

 other valve, in which there is on each side of the rib a cartilage- 

 process, the two cartilage-plates being sometimes united in 

 front, and next to them are situated the raised muscular scars. 

 B. unisulcatus, Matheron (cxviii, 39). 



The presence of a hinge-rib readily distinguishes the present 

 oroup from Radiolites (restricted), and the absence of any other 

 ribs or folds in the attached valve separates it from Hippurites. 



Tamiosoma, Conrad, 1856. 



The type of this genus is a very peculiar fossil from the upper 

 miocene deposits of California, T. gregaria, Conn. Gabb, in the 

 second volume of the Palseontology of California (pp. 61-63), 

 has very ably discussed the organization of this fossil, and 

 comes to the conclusion that it is most likely a species of the 

 Hippuritidse. The specimens which have, up to the present, 

 been found, resemble the elongated, lower valve of Hippurites 

 with a small place of attachment apparently at the thinner or 

 lower end. They are subcylindrical with rather thick walls con- 

 sisting of two or three la3^ers, possessing the same reticulated 

 and striated structure as that of Radiolites, and others. The 

 lower portion of the shell is composed of a large number of 

 irregular chambers or septa which are produced by lateral pro- 

 longations of the inner wall. The end is occupied by a large 

 cavity, similar to the "body-chamber" of Hippurites, but no 

 impressions of teeth have as yet been observed in it. The outer 

 surface is longitudinallj^ striated in the type species which grows 

 in clusters, as does, for instance, H. organisans, Defr. 



In some respects Tamiosoma recalls the organization of the 

 peculiar Hippurite from Jamaica, called by Woodward, Barrettia. 



