322 SPIRIFERIDA. 
at a height 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. 
Atuyris, M’Coy, 1844. 
Etym.—A, without; thuris, a door (7. e. deltidium). 
Syn.—Spirigera, d’Orbigny, 1847. Cleiothyris, King (not 
Phil.), 1850. Huthyris, Quenst., 1871. Actinoconchus, M’Coy, 
1844. 
Distr.—Fossil, about 100 sp.  Silurian—Lias; N. and S. 
America and Europe. A. lamellosa, Lev. (exxxvii, 7). A. 
Roissyt (exxxvii, 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- 
chonellz ; in A. concentrica a slender curved tube is sometimes 
attached to the foramen, beneath the hinge-plate. A. tumida 
has the hinge-plate merely grooved, and the byssal foramen is 
angular. 
KayseErIA, Davidson, 1882. 
Etym.—Named after E. Kayser, a German paleontologist. 
Distr.—K. lens, Phil. (exxxvii, 10-12). 
Distinguished from Athyris by its prominent dorsal septum 
and its connection with the loop, the shape and direction of the 
curved lamellee composing the commencement of the loop, and 
the rounded process by which these lamellz are continued, as 
well as the long extension of the accessory lamelle. 
The continuation of the accessory lamelle 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 Athyris; whilst in the species under con- 
sideration the lamelle arising from the end of the loop are 
extended throughout the whole length of the spiral. 
