8 BRACHIOPODA. 



Order I. Ancylobrachia. 



The oral arms are attached to two shelly plates arising from 

 the hinder or cardinal edge of the ventral valves ; they are re- 

 cimed and convolute on the inner side of the lamina. The animals 

 are generally attached to marine bodies by a tendinous peduncle, 

 which passes through a hole in the top of the umbo of the larger 

 or dorsal valve ; this peduncle and the hole are sometimes obli- 

 terated in the older specimens. 



The order only contains a single family, 



Fam. 1. Terebratulidoe, 



which is nearly synonymous with the smooth Terebratula of 

 Sowerby, the jjerforated Terebratula of Carpenter, the genus 

 Epithyris of PhiUips and Terebratula of King, the family Tere- 

 bratulidm of M'Coy, and Cyclothyrida of Phillips. 



The animal has been described by Linnaeus, Pallas, Owen, 

 Blainville, PhiUppi, D'Orbigny and others. In some genera the 

 hoops are united together below by a transverse band which is 

 attached to medial longitudinal ridges of the ventral valve, as in 

 Terebratula of Retzius := the Terebratella of D'Orbigny, as T. 

 dorsata and Magas, Sow. In others the hoop forms a ring, and 

 is free from the ventral valve, as Gryphus, Megerle^Terebratula, 

 D'Orb. and Terebratulina, D'Orbigny, for T. vitrea and T. caput 

 serpentis. D'Orbigny indicates other genera under the names of 

 Terebrirostra and Fissirostra. 



Order II. The Cryptobrachia 



have the oral arms entirely attached in the form of two or more 

 lobed processes sunk into the grooves in the disc of the ventral 

 valve. They are generally thick shell?. This order also con- 

 sists of only a single family. 



Fam. 1. Thecideada. 

 The animals are described by Philippi and D'Orbigny. The 

 genus Aryiope, De Longchamps = Megathiris, D'Orb. {Tereb. 

 detruncata) is attached by a tendon passing out of a very large 

 perforation below the beak of the dorsal valves : Philippi con- 

 founds this genus with his Orthis, which is different from the 

 Orthis of Dalman. Thecidcea has the shell attached by the trun- 

 cated apex of the dorsal valve, or it is free when the apex is pro- 

 duced and entire. De Longchamps, who estabhshed the genus 

 Argiope in 1839, pointed out the affinity of this genus to The- 

 cidcea. 



Subclass 2. Helictopoda. 



The oral arms are elongate, regularly spirally twisted when in 

 repose. The mantle-lobes are merely applied to the inner surface 



