WOODWARD — HIPPURITID^. 57 



The "ridges" are the smallest difficulty in the structure of the 

 Hippurite, — indeed they form a strong point of analogy with Diceras 

 and Requienia. 



IX. Those authors who have regarded the Hippurites as true 

 Lamellibranchiate Bivalves have not agreed as to their Family-rela- 

 tionship. 



Cuvier placed them with the Oysters, to which they present the 

 strongest analogies ; but from which they differ in having two ad- 

 ductor muscles. 



Prof. Owen adopted Cuvier' s view generally as to the position of 

 the Ritdistes amongst the Lamellibranchiata, and pointed out the 

 difficulty of ascertaining their true characters, on account of the 

 general absence of the inner layer *' which alone receives the im- 

 pressions of the soft parts*." 



M. Deshayes in his latest work {Traite elementaire de Conchy- 

 liologie, Nov. 1848) proposes to include the two families JEtherice 

 and Rudistes in the same gronp, — thus characterized : *' Animaux 

 irregidiers ; manteau ouvert, sans siphons, sans perforations.'* 



I am indebted to Dr. Gray for the opportunity of examining the 

 remains of an authentic example of Mtheria, brought from the Nile 

 many years since by Sir Gardner Wilkinson. The animal is entirely 

 apodal. The body (consisting chiefly of the mass of the liver) has 

 been mistaken for a foot ; it projects backwards, as in Lima and the 

 Scallop. The gills are subequal, and are united behind the body ; 

 they are also united by all their dorsal border to the body and mantle, 

 so as to leave no passage into the dorsal channel and cloaca. The 

 palpi are of a form peculiar to the Iridina of the Nile and some 

 other Unionidce, viz. semi-oval, attached by the straight side, and re- 

 ceiving the gills between their ample and striated inner surfaces. 



Considering the freshwater habitat of JEtheria, the pearly interior 

 of its shell, the absence of hinge-teeth, and its analogies with the 

 Unionidce, I cannot but regard it as a very bad type for comparison 

 with the deep-sea Hippuritidce. 



Prof. Quenstedt (of TiAbingen) in his excellent Handbuch der 

 Petre/aktenkunde (1852), has placed the Hippurites in a more 

 natural position, — between the Chamacece and the Cardiadcef. 



They resemble Chama in being fixed, in the character of the large 

 adductor impressions, and in the well-developed hinge. Three of 

 the five genera further resemble it in the spirality of the upper valve. 

 They also resemble Diceras (a member of the Chamidce) in the 

 adductor muscles being supported by prominent plates. 



There does not appear to me to be any evidence that the mantle- 

 lobes of the HippuritidcR were free. Important as that character is 

 in Malacology, it is of no avail to the Palaeontologist. In the family 

 Mytilidce it is impossible to tell by the shell alone, which of the re- 



* 'Lectures on the Invertebrate Animals,' 1843, p. 287. 



t The late Prof. E. Forbes also adopted this view, in his lectures at the School 

 of Mines in 1853, after examining the British Museum Collection, as he acknow- 

 ledged with his wonted generosity. — Dec. 30, 1854, S. P. W. 



