PLATE VII. 



The following letters refer to the same parts and impressions in evenj fiyure. 



A, adductor muscle {add. longus, Owen) ; r, cardinal muscles {add. brevis and cardinulis, Owen) ; 

 P, pedicle muscles {retractor sup. and inf., Owen) ; J, cardinal process ; L, loop ; T, teeth ; 

 B, sockets ; D, deltidium ; v, vascular impressions ; o, ovarian spaces ; s, septum, &c. 



Fig. 



79. Uncites gryphus. A Belgian specimen, shewing the depressions in the lateral portions of the 



beak, </". 



80. „ „ Profile of the same, a portion of the shell having been removed, so as to 



show that the pouch-shaped depressions do not communicate with the 

 interior of the shell ; g', portion belonging to the dorsal valve ; </", that of 

 the ventral valve. 



81. „ „ Profile of a specimen from Paffrath, in wliich the lateral depressions do not 



exist. 



82. „ ■ „ A young individual from Chimay, considerably enlarged, to show that in the 



young state the shell was fixed by means of a peduncle, issuing from 

 a perforation in the beak of the ventral valve. 



83. „ ,, The extremity of the beak considerably enlarged, to shew the foramen and 



deltidium. 



84. „ „ A horizontal section of the hollow beak. 



85. „ „ Interior of a specimen from Pafi'rath, in the Collection of Professor Beyrich, of 



Berlin, exhibiting traces of the spiral lamellae which supported the arms. 

 This sketch was kindly communicated to me by M, Suess, of Vienna, with 

 Professor Beyrich's permission. 



86. „ „ A specimen from Chimay, showing the position of the pouch-shaped ex- 



pansions (</", those belonging to the ventral valve), and the attachment of 

 the crural lamellae forming the spires. 



87. Atrypa RETICULARIS, Linn., sp. The first-mentioned type of Dalman's genus ^^>-y/)«, and of his 



first division striates; in this Silurian example no trace of the foraminal 

 aperture is visible. 



88. „ „ from the Eifel, exhibiting in the most beautiful manner the foramen and 



deltidium. 



89. „ „ Interior of dorsal valve, showing the natural position of the spiral cones. 



90. ,, „ Interior of ventral valve, from a specimen discovered by M. de Koninck (now 



in the British Mus.), and in which the vascular impressions are beautifully 

 illustrated. 



91. „ „ Interior of dorsal valve, from which the spires have been removed, in order 



to exhibit the portion of the quadruple impressions left by the adductor 

 muscle. 



92. „ ,, Interior, from which the largest portion of the shell of the dorsal valve has 



been removed, to shew the position and shape of the spiral cones; from a 

 beautiful example in the cabinet of Prof. Buckman. 



93. „ „ A transverse section, to show the extent of space occupied by the spiral cones; 



M, ventral ; n, dorsal valve. 



93 bis. „ marginalis, Dalman, sp. 



94. ,, prunum. Type of Dalraan's 2d section tet>e5. 



95. Steingocephalus BuRTiNi. Exterior, showing foramen and deltidium. 



96. „ „ A young example from Belgium, with large triangular aperture. 



97. „ „ A fragment of the interior of both valves, from a specimen in the 



collection of M. de Koninck : J, cardinal forked process ; c, portions 

 of the stems or origin of the loop. (See pp. 74 and lb, for figures 

 of the loop.) 



98. „ „ Fragment of the dorsal valve, to illustrate the hinge plates, crura of 



the loop, cardinal process and quadruple impression of the 

 adductor. 



