A MARINE EARLY CRETACEOUS FAUNA. 13 
Hitherto Iotrigonia has been recognised with complete certainty 
only in India and South Africa. The valid species of the genus 5 include 
I. vau (Sharpe) and I. stowi (Kitchin) from the Uitenhage beds of 
South Africa ; I. crassitesta van Hoepen, I. inconstans van Hoepen and 
I. kaughfoni Rennie from Zululand; and I. v -script a (Kitchin) and, 
doubtfully, I. dubia (Kitchin) from the Oomia beds of Kachh in India. 
Kitchin refers to Trigonia kuhni Muller from Neocomian beds in 
Tanganyika as possibly related. I have not seen Muller ’s work. 
Of the American early Cretaceous species to which attention was 
drawn by Kitchin, Trigonia diversicostata Whiteaves, from Queen 
Charlotte Islands, and Trigonia heterosculpta Stanton from Patagonia 
are, I think, generically distinct. They and certain forms from the 
Malone Formation in Texas (Cragin, 1905, pi. LX, figs. 4-6) give more 
the appearance that Y-ribbing developed as a sudden late acquisition, 
and it never assumes the perfect Y of the Indian and African species. 
Chilean forms described by Phillipi ( T . arsinoe P. and T. foveata P.) 
and an Alaskan species (T. doroschini Eichwald) also are mentioned 
by Kitchin, though he does not stress close relationships. I have not 
seen these two works. 
The vertical ranges of Iotrigoma , from the African and Indian 
records, is a little difficult to assess. Spath’s monograph on the 
ammonites (1930) establishes definitely that the age of the Uitenhage 
species is Yalanginian. Of the Zululand forms I. crassitesta and /. 
inconstans occur in the Ndabana beds which lie below the ammonite- 
rich Umsinene beds of Albian age. Yan Hoepen (1929 A, p. 10) refers 
them to the Aptian, but the evidence for this is not yet published- — the 
only ammonite in his list is Douvilleiceras sp., presumably Douvilleiceras 
in a comprehensive sense. As Rennie points out, all the Ndabana 
Trigonias are closely akin to Uitenhage species. I. haughtoni from 
Northern Zululand was found below a horizon with an Aptian ammonite 
( Tropaeum sp.) ; but whether it is Aptian or pre-Aptian remains to 
be proved. 
Similarly in Kachh, in India, the evidence is not precise. The 
species of Iotrigonia are from the Oomia group, the Trigonia bed 
occurring above the zone with Tithonian ammonites and below the 
beds with Aptian ammonites (see Spath’s analysis of the succession — 
1933, pp. 736-757). Thus there the genus may be of late Tithonian or 
some pre-Aptian Cretaceous age. Once again the resemblance of associ- 
ated Trigonias to Uitenhage species has been noted by Kitchin and 
others. 
Thus at present all that can be stated without question about the 
range of Iotrigonia is that it is not known earlier than Kimmeridgian 
or later than lower Aptian. But there is reason to believe that it may 
be confined to beds of Yalanginian or near- Yalanginian age. It is 
5 Bibliographic references to these and other species mentioned are as follows: — 
I. vau : Sharpe 1856, p. 194, pi. XXII, fig. 5, redescribed by Kitchin 1908, p. 110, 
pi. VI, figs. 1-3. I. stowi: Kitchin 1908, p. 115, pis. VI, figs. 4, 5; VII, fig. 1, 
I. crassitesta : van Hoepen 1929B, p. 7, pis. II, figs. 4, 5; III, figs. 1, 2. I. incon- 
stans: van Hoepen 1929B, p. 8, pis. Ill, figs. 3, 4.; IV, figs. 1, 2. I. haughtoni: 
Rennie 1936, p. 340, pi. XLI, figs. 1-4. I. v-scripta: Kitchin 1903, p. 70, pis. VII, 
figs. 6-8; VIII, figs. 1-3. I. clubia: Kitchin 1903, p. 67, pi. VII, figs. 3-5. Trigonia 
diversicostata: Whiteaves 1876, p. 68, pi. IX, fig. 1. Trigonia heterosculpta: 
Stanton 1901, p. 20, pi. IV, figs. 16-18. 
