K. L. Prexdergast. 
:v2 
Girty (1908, p. 264) compares his species Productus signatiis with 
P. opuntia. The fig’ures are not clear, but give an impression of an ornamen- 
tation of Cancrinella rather than of Krotovia or \Pustula. The spine bases 
are heavy and elongated, and Girty himself says that on some of the casts 
irregular lirae can be seen between the spine bases. The species is distinct 
from K. spinulosa. 
The characters distinguishing the other species of this genus, Krotovia 
micracantha and Krotovia senticosa, from this species are dealt with in the 
description of those species. 
AULOSTEGES llelnierseii. 
1847. — Ilelinerscn. Leonhard & Broun ’s Jahrbuch fiir Mineralogie p. 331, 
text-figure. 
Genotype. — Anlos1< ge,^ variabiUs Helmersen = Orthis wangenheimi (Ver- 
neuil). Helmersen 1847, Leonhard and Broun ’s Jahrbuch fur Mineralogie, p. 
331, with text-figure. 
Diagnosis. — Medium to large shells, ovoid to quadrangular or triangular 
in outline. Concavo-convex or platy-convex dorso-ventrally. Ornamentation 
essentially spinose with development of radial lirae or concentric wrinkles. 
Pedicle valve convex with well-developed area and pseudo-deltidium. 
Umbo ])ointed, possibly deformed or with cicatrix of attachment. Edentu- 
lous. Shell with median sinus. 
Brachial valve flat or concave, without area or area narrow and linear. 
Cardinal margin produced into triangular extension medially. Median septum 
separating dendritic muscle impressions. Pattern of brachial impressions 
productiform. Cardinal process large, inclined or horizontal. 
Description. — The shells of this genus are usually massive although 
there is a great variation within the genus. They vary in shape from oval 
to quadrangular and triangular, the hinge-line being less than the greatest 
width of the shell. Neither the i^edicle nor the brachial valve is produced 
into distinct ears. 
The pedicle valve is regularly convex or geniculate. Ti’ansversely it is 
depressed by a median sinus which commences some distance behind the 
umbo, is strongest in the centre of the shell and flattens out towards the 
anterior margin. The area is triangular and usually well-developed, it is 
marked by vertical or longitudinal striations and may he flat or concave; 
the concavity may not be regular and a sudden change in curvature gives 
the recurved area seen in A. s})inosus, Hosking. A narrow ]'>seudo-delticl!uiu, 
triangular or parallel-sided, divides the area. In some specimens, for instance 
Aulosteyes ivangenheimi (Verneuil), small s])ines are present on the pseudo- 
deltidium. These are not seen in all other species, but their occasional oc- 
currence suggests that their absence is secondary, due to removal. The umbo 
is sharp and pointed, and usually erect. AVhere, howevei’, the umbo has been 
deformed by attachment, it may be twisted to one side or produced across 
the area {see, for example, Aulosteges haracoodensis Eth. til., 1914, pi. iv, 
fig. 13). The surface of the valve is ornamented by spines, erect and/or 
adherent, and may be concentrically wrinkled on the visceral disc. Radial 
lirae are seen in some of the species, e.g., A. ivolfcampensis King and A. 
medlicottianus Waagen, while stronger radial markings ornament the trail in 
A. tibeticus Diener. 
