C. E. Beecher — Revision of the Families of Loop-hearing, etc. 377 



Eucalathis, do not represent the highest development of the family 

 type, but must be regarded as degraded forms. Among fossil 

 genera, Cryptonella, Megalanteris, Dielasrna, Centronella, Hens- 

 selmria, String ocepTialiis, and some others, probably belong here. 

 The following subfamilies can be recognized: (1) the Centronellinoe, 

 (2) String ocephalinoe, (3) TerehratuUnce, and (4) DiscoliinoB. The 

 adult arm structure in Discolia is homologous with early larval 

 features in Terebratulina ; also the cirri are centrifugal, or directed 

 outwards, as in early stages of Terebratulina, and not centripetal 

 as in larval Magellania. 



The TerehratellidcB. 



The loop in the second family, for which the name Terebratellidae 

 is retained, undergoes a series of metamorphoses while attached to 

 a dorsal septum during the larval and immature stages of the 

 animal, and in the higher forms results in a loop of secondary 

 growth much like the primary loop of some of the early genera of 

 the Terebratulidae. The cirri in larval stages of the animal are cen- 

 tripetal, or directed inwardly. 



In one division of the Terebratellidse, the stages of growth may 

 be correlated with the adult loops in the genera Gwynia, Cistella, 

 Platidia, Ismenia, Milhlfeldtia, Terehratalia^ and Dallina^\ while 

 in another division a quite different series of transformations takes 

 place. These have been termed by Fischer and OEhlert,^ the proe- 

 magadiform, onagadiform, magaselUform, terehratelliform, and mag- 

 ellaniform stages, from their resemblance to the loops of the genera 

 suggesting these names. The prceniagadiform stage is here divided 

 into the bouchardiform and megerliniform stages. To these may 

 be added the earlier larval stages resembling Giuynia and Cistella, 

 as in the previous group, and showing a parallel development in the 

 first two stages. 



These two groups of the Terebratellid^e usually have been con- 

 sidered as part of the family Terebratulidae, although King^ "* in 1850 

 proposed the name Terebratellidse to include Terehratella, MiXhl- 

 feldtia, and Ismenia, on account of the attachment of the loop to 

 the septum of the dorsal valve in these genera. Friele" and Des- 

 longchamps^ next showed that Macandrevia cranium and Dcdlina 

 septigera passed through a series of changes in which the loop was 

 united to a septum in all but the last stage. This completed loop in 



* Type Terehratula transversa G. B. Sowerby. f Type Terebratula septigera Loven. 



