BRACHIOPODS. £47 



Oeder II. — ARTICULATA. 



The Articulata, or Testicardinia, have the valves articulated by a hinge, usuully 

 formed by teeth on the lower valve, fitting into sockets in the upper one. The 

 intestine ends blindly. On the inner surface of the upper valve a more or less compli- 

 cated calcareous loop, the object of which is to support the arms. In the existing 

 forms this loop is usually quite simple, but in some of the fossils it is very complicated, 

 portions being coiled in a spiral, which evidently supported all parts of the arms, so 

 that their extension from between the valves was impossible. In the living forms a 

 slight protrusion may be occasionally seen. 



Passing by the three extinct families, Peoductid^e, Calceolid^, and Orthid^, we 

 reach first the family Rhynchonellid^, of which forms are represented in the northern 

 seas. In these the arms are coiled in a spiral ; the shell is either free or anchored by 

 a peduncle, which passes through an opening in the beak of the larger valve. The 

 hinge line is either curved or straight, and the outer surface of the shell is impunctate. 

 Rhynchonella psittacea is a common form in the colder waters of the northern hemi- 

 sphere, from the Gulf of Maine to Europe. Other species are found in Japan, New 

 Zealand, Fijis, etc. 



The Spiriferid^ attained its greatest development in the paleozoic rocks, disap- 

 pearing in the Jurassic. In these forms the shells are unequal, have a straight hinge 

 line, while the support for the arms is coiled in two spirals, much like a watch-spring. 

 Occasionally these spirals bear hardened supports for the tentacles, 

 thus indicating that these parts could have but the slightest 

 motion. 



The Teeebeatulid^ is the largest of the recent families. In 

 these foi-ms the arms are not coiled in a spiral. The shell is punc- 

 tate and ventricose, the lower valve is perforated for the passage 

 of the peduncle, and the two valves are hinged together by two 

 teeth. On our New England coasts, Terebratulina septentrionalis 

 is the most abundant, being brought up by the dredge from 

 a depth of only a few fathoms. Usually the specimens are en- 

 crusted with a yellow sponge. In life the animal has considerable '^"'' s^ieMi^S."""" 

 powers of movement, raising itself at times so that it stands upright 

 upon its peduncle, or twisting itself around upon the same support. In the more 

 northern waters of America the genus Waldhaniia is found, while the genus Thecid- 

 ium is found in the Mediterranean and the West Indies. 



These forms are popularly known as lamp shells, their rounded shell, with its per- 

 forated beak, presenting no inconsiderable resemblance to the lamps used by the 

 ancients. The existing species possess no inconsiderable vitality, and Professor Morse 

 has called attention to the striking fact that the power of the recent species to with- 

 stand adverse circumstances has a curious parallel in the history of the group, the 

 Lingula of the Potsdam sandstone being congeneric with the forms living in Japan 

 and the Carolinas to-day. 



J. S. Kingsley. 



