I 



[ 63 ] 



from one sui'fao<' to the otbei*, for the most part in a vertical 

 direction, and iit tolerably regular intervals ; but, just before, 

 terminating near tbe outer surface of tbe epidermis, their tubular 

 orifices suddenly became dilated, the lower half of the canal was 

 often considerably smaller in diameter than the upper half. The 

 canals were occupied by coecal processes proceeding from the 

 mantle or fleshy covering of the animal. Their functional nature 

 was, according to Dr. Carpentei-, bi-anchial in their ofiice, and 

 subsei-vient to respiration ; but, as observed by Professor King, the 

 outer epidermis, which covered their expanded termination, would 

 seemiugly i^revent any communication between the surrounding sea 

 water and the mantle, so that it might be questioned whether they 

 ■were at all connected with the respiratory function. In certain 

 genera, such as Lingula, there were no canals, the shell being found 

 to consist of flattened prisms of considerable length, and which lay 

 parallel to one another with great regularity, and at a very acute 

 angle. The shell substance was also either almost entirely 

 composed of a horny or of a calcareous substance. 



INTERIOR OF VALVES. 



Having described the exterior of the shell, he must add a few 

 words with respect to the interior. On the inner surface of both 

 valves several well defined muscular impi-essions were observable ; 

 these varied considerably in position and shape in diiferent species. 

 They formed either indentations of greater or lesser size and depth, 

 or occurred as variously shaped projections. In the Trimerellidce 

 some of the muscles were attached to a massive or vaulted platform 

 situated in the medio — longitudinal region of the posterior half or 

 umbonal portion of both valves. In addition to these there existed 

 in the interior of the dorsal valve, in some genera a variously 

 modified thin calcified ribbon- shaped lamina or skeleton for the 

 support mainly of the brachial or labial appendages, and so varied 

 and constant were these in shape to certain species that this 

 laminal apophysis had sei'ved as one of the chief characters 

 in the creation of both recent and extinct genera. In certain forms 

 the lamina was more or less developed, and so bent as to assume the 

 shape of a loop. The loop was in some genera attached only to the 

 hinge-plate, as in Terebratula, Waldheimia, &c.. In others likewise 

 so to a central longitudinal plate or septum. In certain families 

 tbe apophysis presented the form of two spiral processes, which 



