BllAClIWPODS. 



247 



Okdei; II. 



ARTICULATA. 



The Avticulata, or Tosticardiiiiii, have the valves articulated by a hinge, usually 

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

 intestine end.s blindly. On the inner surface of the vipper 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 imjiossilile. In the living forms .i 

 slight protrusion may be occasionally seen. 



Passing by the three extinct families, Productid.e, Calc'eolidjj, and Okthid-e, we 

 reach first the family Rhynchoxellid-e, 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. 

 Ehi/nehone.llapsittacea is a common form in the colder waters of the northern hemi- 

 sphere, from the Gulf of Maine to Europe. Other sjieeies are found in Jap.an, New 

 Zealand, Fijis, etc. 



The Spiijifeiud.e attained its greatest develoiiment in the paleozoic rocks, disap- 

 ])earing 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 Terebkatuliu.e is the largest of the recent families. In 

 these forms 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 Enghuid coasts, Terebratulina septentrionalh 

 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 

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

 upon its peduncle, or twisting itself around upon the same sup])ort. In the more 

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

 iii,m is found in the Mediten-anean and the West Indies. 



These forms are popularly known as lamp shells, their roundi'd sliell, with its ])er- 

 for.ated Ijeak, 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 jiower of the i-ecent species to with- 

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

 Li/ir/idaoi the Potsdam sandstone being congeneric with the forms living in .Japan 

 and the Carolinas to-day. 



J. S. Kl>GSLEY. 



<eptentrionalis. 



