MAZATLAN TTNIVALVES 



247 



had et umbilico spiraliter liratis ; ad peripheriam carina acutd, 

 prominente, altera spiram ascendente, minus prominente ; inter 

 eas suturd valde impressd ; aperturd anfr. penult, vix ad cari- 

 nam attingente. 



TKis very remarliablo sliell lias tlie general appearance of 

 Helix (Iberus) Gualterianus. It has however two keels, (that 

 on the spire being less prominent) and a deep rather narrow- 

 umbilicus. The whirls rapidly increase in size both in breadth 

 and thickness. The generic position is doubtful, the only 

 specimen found haviag lost the greater portion of the last 

 whirl. The general aspect and texture are like a very large 

 Vitrinella, and the usual unformed portion is clearly defined, 

 being much larger than in the t>i)ical species ; it differs how- 

 ever in the comparative length of the adult part, which must 

 have consisted of at least two complete whirls. The shell 

 when perfect may have been "2 in length: the penultimate 

 whirl measures long. "03, lat. "CMj by '025, div. 180". 



^a5.— Mazatlan ; 1 broken specimen off Spondylus calcifer ; 

 Upool Col. 



Tablet 1162 contains the specimen. 



312. PVlTBINELLA OEBIS, 71. S. 



? V. t. discoided, diaphand, liyalind ; valde complanatd, 

 spird planatd, hasl subplcmatd ; ad poripheriam rotundatam, 

 et intus umhiUcum apertissimum, strlis spiralihus paucis, plus 

 minusve imjiressis ; infra-et supra Icevi, interdum stria spirali 

 juxta suturam hand impressara ; anfraciu ultimo penultimum 

 parum attingente ; aperturd angustd, sjnraliter elongatd, suh- 

 quadratd ; lahro sinuato, postice producto. 



This singular species has relationship to Discohelix, Dicr. 

 PaZfl?o?«<. i. 132, = Orbis, Lea; of which, as of Vitrinella, the 

 animal is unknown, being classed with Littorinida; by Phil. 

 Sandb. Conch. p.'l74, but with Architeetonicida) by I£. ^ A. 

 Ad. Gen. i. 2M. It has the appearance of the common flat 

 Dundry Ammonites, with the periphery rounded and spirally 

 striated. A beautifully perfect specimen, quite transparent, 

 but probably immature, was found inhabiting the spu-al portion 

 of a dead Isapis macidosa, the mouth of which had been choked 

 up with coralline, among the debris of a Spondylus. It 

 measures long. "0075, lat. '033 by "027, div. 180". Three 

 other broken specimens were found on Chamse. 



