126 MOLLUSCA. 



most highly developed in Palaeozoic time. Of the articulated 

 genera, those having spiral arms appeared first ; those with cal- 

 careous spires disappeared with the Lias. Braehiopods furnish 

 the most numerous instances of recurrence, owing to their tenacity 

 of life, some species persisting through a whole geological for- 

 mation. The genus Lingula has existed since the Cambrian. 

 " Of the families of the Brachiopoda, the ProductidcB and 

 Strophomenidce are exclusively Palaeozoic. The Spiriferidce are 

 mainlj^ Palaeozoic, but extend into the Lias, w^hei'e they finally 

 disappear. The LingulidcB commence in the Cambrian period, 

 and have survived to the present day. The RhynchonelUdce, 

 CrmiiadcB and Discinidce commence in the Silui'ian period, and 

 are represented by living forms in existing seas. The Koninck- 

 inidce are exclusivel}' Triassic. The ThecididcB extend from the 

 Trias to the present day ; and the Terehratulidm appear to com- 

 mence in the Devonian, and are well represented by living forms." 

 (Nicholson). 



ORDER ARTHROPOMATA. 



Valves united along a hinge-line, articulating by hinge-teeth ; mantle lobes 

 not free ; intestine ending csecally (no anal aperture). 



FAMILY TEBEBRATULID^. 



Shell minutely punctuate, usually round or oval, smooth or striated ; the 

 ventral valve having a prominent beak with a foramen; two curved hinge- 

 teeth; the arm-supports having the form of a loop. 



No. 355. Terebratula grandis, Blum, 



The shell of this genus is smooth and convex; 

 the beak perforated ; foramen circular; deltidium 

 of two pieces; loop simple. Eight species are 

 found living, and many fossilized since the Trias- 

 sic. From the Miocene Tertiary of Bande, 

 "Westphalia. 



