436 Mr. J. E. Gray on the AiTangement of the Brachiopoda. 



3. ScLEROBRACHiA. The Oral arms supported by a shelly plate 

 arising from the hinge-margin of the ventral valve. 



4. Sarcicobrachia. The oral arms fleshy, without any shelly 

 support. 



C. ? The animal unknown ; perhaps Conchifera. 



5. RUDISTES. 



Subclass 1. Ancylopoda. 



The oral arms not extensile or only at the tip ; on fixed shelly 

 supports, or in grooves in the under or ventral valve ; the mantle 

 is adherent to the shell, the substance of the shell being pierced 

 with numerous minute perforations, which are pervaded by the 

 processes of the mantle. 



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 recurved 

 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 obliterated in the older specimens. 



The order only contains a single family. 



Fam. 1. Terebratulid^, 



which is nearly synonymous with the smooth Terehratula of 

 Sowerby, the perforated Terehratula of Carpenter, the genus 

 Epithyris of Phillips and Terehratula of King, the family Tere- 

 hratulidcB of M^Coy, and Cyclothyridce of Phillips. 



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

 Blainville, Philippi, 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 Terehratula 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 = Terehratula, D'Orb., and Terehratulinay D'Orbigny, 

 for T. vitrea and T. caput serpentis. 



D^Orbigny indicates other genera under the names of Tere- 

 hrirostris and Fissirostris. 



Order II. The Cryptobrachia 



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

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

 They are generally thick shells. This order also only consists of 

 a single family. 



