30 
K. L, PRENDERGAST. 
develop which are connected with the spines.’' Krotovia then includes speci- 
mens with incipient plications thus overlapping with Avonia Thomas. 
Paeckelmann (1931, p. 77) has emphasised this fact, and distinguished 
Avo7iia s.str. and Krotovia as subgenera of Avonia Thomas, the forms to be 
separated by the presence {Avo^iia) or absence {Krotovia) of costae. The 
distinction is thus purely arbitrary, the two genera intergrading. 
1932 . — Pusiula senticom Hosking, p. 47, pi. iii, figs. 2-3. 
Syntypes. — G.S.W.A. 1/4970 (a), from Creek 1 mile west of Callytharra 
Springs, Wooramel River. Callytharra Limestone 
Biag^iosis. — Thin-shelled form, outline semi-circular to subquadrate, 
hinge-line less than maximum breadth. Pedicle valve gently convex, non- 
sinuate, auriculate, umbo pointed and incurved. Brachial valve strongly 
concave; visceral cavity of Productus typici ^ type. Ornamentation on both 
valves of erect spines in irregular quincunx and fine concentric lamellae. 
Internal features of pedicle valve unknown, brachial valve with short, 
broad cardinal process continuing into short median septum. : 
Description. — See Hosking, 1932, pp. 47-49. i 
Pemarks. — The type specimens of this species have a convex pedicle i 
valve with a concave brachial valve, the visceral cavity between the tw^o 
being very thin. Also, as Miss Hosking says in her description (p. 48) “the 
lack of any marked concentric ornamentation is one of the chief features of 
the species.” The specimens must, then, be referred to Krotovia rather than 
to Pustula. 
1932 . — Pustula micracauiha Hosking, p. 49, pi. iv, figs. 4a, b. 
Syntypes: — G.S.W.A. 1/4970 (b), from Creek Vj mile west of Callytharra 
Spring, Wooramel River. Callytharra Limestone. 
Diagnosis. — Small, thin-shelled form. Shell outline semi-circular to sub- 
quadrate, hinge-line slightly less than greatest shell breadth. Pedicle valve 
geniculate, non-si nuate; umbo small, not overhanging hinge-line. Brachial 
valve deeply concave and geniculate, closely following contour of pedicle 
valve ; visceral cavity of Productus typici ^ type. Ornamentation on pedicle 
valve of recumbent spines in irregular quincunx with concentric folds pos- 
teriorly and on ears. 
Short median septum in brachial valve. Other internal features not 
known. 
Description. — See Hosking, 1932, pp. 49-50. 
Remarks. — From an examination of the type specimens there can be no 
doubt that this species should be referred to Krotovia. The visceral cavity is 
thin, the concentric wrinkles are not pronounced and the nearest British form 
is P.spiniilosus J. Sow., the genotype of Krotovia. 
1814 . — Productus spinulosus J. Sowerby, p. 155, pi. Ixviii, fig. 3. } 
1860 . — Productus spinulosus J. Sowerby, Davidson, p. 182, pl. ii, figs. 23, 24. [ 
Krotovia senticosa (Hosking) . 
Krotovia micracantha (Hosking). 
Krotovia spinulosa (J. Sowerby). 
PI. iv, figs. 11-13. 
I 
