LAMP-SHELLS. 



43i 



Hingeless Group. 



UPPER VALVE AND ANIMAL OF 



Crania (magnified). 



very remarkable by the long, spirally -coiled and calcified arms. Spirifer was 

 very abundant in the Palaeozoic epoch, but died out with the Lias. 



The second order of the Brachiopods (Ecardines), or those whose 

 shells are without hinges, consists of but four families, two of which 

 may be briefly described. The unstalked genus Crania is widely distributed, 

 both geologically and at the present time. Its structure is so peculiar that it 

 forms a family by itself (Craniidee). The shell is attached to some submarine 

 object by the ventral valve ; the dorsal valve is lid- 

 like, and the two valves connected, not by a hinge 

 or interlocking processes, but simply by muscles. The 

 best-known of the four living species (here figured) of 

 the northern seas, is almost always found in company 

 with Terebratulina, which, however, it does not follow 

 into the seas of Northern America. , 



The last family to be described, the Lingulidce, 

 is also one of the most interesting. It existed in 

 the oldest fossiliferous strata, and is still found living 

 chiefly near the shores of the warmer seas. It may be regarded as perhaps the 

 very oldest of the Brachiopods. Indeed, if we may look upon the hinge which 

 characterises the other order as a specialisation, the hingeless forms are clearly 

 the older and more primitive. The shell of a Lingula is thin and horny, almost 

 flexible, and green in colour. The valves are almost exactly similar, and, as we 

 have seen, they are not hinged together ; and, further, they have no processes for 



the support of the thick, fleshy spiral arms. No 

 living Lingula is now found in European seas, but 

 L. pyramidata occurs on the American coasts, and 

 another, L. anatina, in the Philippines. The stalk 

 of the former, which is nine times as long as the 

 bod}-, does not become attached, but moves like a 

 worm, and again, like certain worms, makes tubes 

 out of sand into which it can withdraw. The 

 Lingulidai generally live in holes in mud, the 

 bottom of which is lined with sand. The shell- 

 covered body projects above the mud to open and 

 feed ; on being alarmed, it shuts and disappears 

 below the surface. The cilia at the mantle-edge 

 form a fine sieve which prevents foreign particles 

 from entering the gills. The length of life of L. 

 'pyramidata is not more than a year. The sim- 

 plicity of the shell of Lingula, which may best be 

 compared with the cartilaginous structures at the 

 anterior end of a chsetopodous annelid, and its occurrence in the oldest strata in 

 which Brachiopods are found, seems to justify the conclusion that it stands nearest 

 of all the class to the worm-like ancestor. 



H. and M. BERNARD. 



Lingula pyramidata (nat. size). 



