218 SOLARIID^. 



carina the basal margin of the aperture is deeply flexuously 

 emarginate ; above the carina it is again, but less deeplj'^, emar- 

 ginate, then sweeps forward roundly, and then slightly recedes 

 before joining the preceding whorl. This curious form belongs 

 in all probability to the Solariidffi, representing among them 

 Basilissa among the Trochidse, and recalling Platyschisma, but 

 "with a different aperture. When perfect, the margin at the 

 carina must project forward like a claw or nail, as in Schizos- 

 toma. When adult, the nuclear whorls are filled up with a solid 

 deposit of shelly matter, and it is probable that there is a slight 

 notch at the end of the umbilical rib. S. brunnea, Dall. West 

 Indies. 



Platyschisma, M'Coy. 



Distr. — Silurian — ; U. S., Europe. P. Uchtensis, Keys 

 (Ixv, 1). 



Shell depressed trochiform, whorls somewhat rounded, orna- 

 mented with small transverse ribs ; spire short, whorls few ; 

 aperture oblique ; umbilicus small, rounded. 



Architea, Costa. 



Syn. — Trachysma, Jeffre3^s. 



Distr. — A. delicatum, Pliil. (Ixv. 8). 



Shell turbinate, but little elevated, thin, widely and deeply 

 umbilicated below; aperture rounded, peristome continuous, 

 simple. Operculum corneous, pellucid, spiral, flattened and 

 smooth on the outer side, the spire slightly prominent in the 

 centre of the inner side. 



Straparollus, Montfort, 1810. 



Syn. — Euomphalus, Sowb. Helicotoma, Salter. Pleuronotus, 

 Hall. Helicites, Schloth. Centrifugus and Inachus, His. 

 Cirrus, Sowb. Phanerotinus, Sowb. (partim). Omphalocirrus, 

 Planicirrus, Echinocirrus and Trochocirrus, Ryckholt. Omphal- 

 otrochus, Meek. Phymatifer, Kon. Straparollina, Billings. 



Distr. — 60 sp. Lower Silurian to Trias ; United States, Europe, 

 Australia. S. Gualteriatus, Vern. (Ixv, 9). S. calcar, d'Orb. 

 (Ixv, 21). 



Shells depressed, whorls angular or carinated, aperture sub- 

 quadrangular, umbilicus wide, conical. Opercuium shelly, multi- 

 spiral. 



It has been proposed by several conchologists to unite the 

 genera Straparollus (= Euomphalus) and Solarium in one. 

 When, however, we compare the large number of species of both 

 these genera, it appears that the smooth or at least less orna- 

 mented surface of the shell, the constant want of a distinctly 

 crenulated margin round the umbilicus, combined with the 

 roundish form of the whorls of Straparollus, make its separation 



