BRACHIOPODA. 103 



in palaeozoic faunas in which the accessory lamellae attain so high a develop- 

 ment. As already observed, Bittner has detected a number of such 

 double-spired forms in the Alpine Trias, over all of which he extends the 

 generic term Athvris (or Spirigera), though he has introduced for them a 

 number of subordinate names based upon slight differences of structure, as 

 follows : 



Pexidella ; smooth forms with thickened shells, and loop of inconspicuous 

 size. 



DiPLOSPiRELLA ; smooth forms without shell-thickening and with prominent 

 loop. 



EuRACTiNELLA ; cinctured forms with slightly developed area and broad ribs 

 separated by deep, narrow furrows. 



Anisactinella ; forms with alternating ribs, area and elevated deltidium. 



The duplication of the spirals has also been observed in other Triassic genera, 

 notably Koninckina, Suess, and Amphiclina, Laube;* shells differing from 

 Katseria and its Triassic allies in so many other points of structure that a close 

 phyletic connection between them seems highly improbable. 



Genus RETZIA, King. 1850. 



PLATE L. 



1845. Terebratula, us Vbrmboil. Bull, de la Soc. geol. de France, second sei„ vol. xi, p. 471, pi. xiv, 



figH. 10 a-d. 

 1850. Retzia, Kino. Moiiogr. Permian Fobs. Kiigland, p. 137. 

 1854. Retzia, Davidson. Introd. British Fossil Brachiopoda, \i. 88, pi. vi, fig-. 77. 

 1886. ijetzio, (Eh LKRT. Annales Sci. Geol., volxix, No. 1, p. 24, pi. xi, figs. 11-19. 



" A Spiriferidia ; in general oval longitudinally ; ribbed or striated ; with 

 long punctures. Large valve foraminated at or near the apex of the umbone ; 

 with a triangular area, and a closed fissure. Type Terebratula Adrieni, De Ver- 

 neuil." (King, Monogr. of the Permian Fossils of England, p. 137.) 



The term Retzia has come into general use as a designation for palaeozoic 

 brachiopods which have an elongate-ovate form and radially plicated exterior. 



* See Ladbb, Die Fauna der Scbichten yon St. Cassian, Zvreit. Abtheil., p. 28. 1865. 

 Bbbchbr, American Journal of Science, vol. xl, p. 211, pi. ii. 1890. 



