322 SPIRIPERID^. 



at a lieiojht of about one line, curves forward. The two then 

 unite and form a single band, which extends forwards to about 

 the front of the coil, and there ends in an obtuse point." — BiL- 

 LINGS. 9 sp. Silurian, Devonian — Trias; Europe and North 

 America. S. heteroclita, Defrance cxxxvii, 4, 5 . 



MiMULUS, Barr. Shell like Spirifer, but the smaller valve with 

 a sinus, the larger one with a saddle ; interior unknown. S. 

 perversa, Barr. Silurian ; Bohemia. 



Athyrts, M'Coy, 1844. 



EtyTYi.' — A, without; thuris, a door {i. e. deltidium). 



Syn. — Spirigera, d'Orbigny, 184'7. Cleiothyris, King (not 

 Phii.), 1850. Euthyris, Quenst., 18*71. Actinoconchus, M'Coy, 

 1844. 



Distr. — Fossil, about 100 sp. Silurian — Lias ; N. and S. 

 America and Europe. A. lamellosa, Lev. (cxxxvii, 7). A. 

 RoiHsyi (cxxxvii, 8, 9). 



Shell impunctate, transversely oval, or suborbicular, biconvex, 

 smooth, or ornamented with squamose lines of growth, some- 

 times developed into wing-like expansions ; hinge-line curved, 

 area obsolete, foramen round, truncating the beak, deltidium 

 obsolete ; hinge-plate of dorsal valve with four muscular cavities, 

 perforated by a small round foramen, and supporting a small 

 complicated loop (?) between the spires ; spires directed out- 

 wards, crura united by a prominent oral loop. 



The foramen in the hinge-plate occupies the situation of the 

 notch through which the intestine passes in the recent Rhyn- 

 chonellffi ; in A. concentrica a slender curved tube is sometimes 

 attached to the foramen, beneath the hinge-plate. A. tiimida 

 has the hinge-plate merely grooved, and the byssal foramen is 

 angular. 



Kayseria, Davidson, 1882. 



Etym. — Named after E. Kayser, a German palaeontologist. 



Distr.— K. Icns^ Phil, (cxxxvii, 10-12). 



Distinguished from Athyris by its prominent dorsal septum 

 and its connection with the loop, the shape and direction of the 

 curved lamellae composing the commencement of the loop, and 

 the rounded process by which these lamellae are continued, as 

 well as the long extension of the accessory lamellae. 



The continuation of the accessory lamellae from their com- 

 mencement at the loop to the end of the spiral is especially 

 notable. In Meristina there is a simple loop; in Whitfieldia this 

 loop is continued by a bifurcation ; this bifurcation is still 

 further continued in Athj'ris ; whilst in the species under con- 

 sideration the lamellae arising from the end of the loop are 

 extended throughout the whole length of the spiral. 



