414 R. Bullen Neicion — Fossils from Saratcak, Borneo. 



There appear to be two Cretaceous species with which this form 

 may be confounded, viz., A. pectinata, Schlotheini, sp., and 

 A. carinnta, Lamarck, sp. The former, however, has more 

 oblique lateral surfaces and is more strongly arched ; the dorsal 

 area is not flattened, but bears numerous V-shaped ribs, which 

 extend from the side plications, forming irregular grooves or canals. 

 A. carinata possesses deeper and more compressed valves, and 

 a much narrower dorsal region, which although rather similarly 

 ribbed at intervals, yet differs from the present species in having 

 prominent, elevated, and curved points forming the dorso-marginal 

 terminations of the numerous lateral plications. 



A form of this genus {A. Mm-tnptirensis) has already been 

 described from the Cretaceous rocks of Southern Borneo, which 

 differs from the present shell in possessing a keel-like back 

 formed by the meeting of the lateral plications in that area. 

 Excellent figures of A. amor have been published, but those 

 given by Goldfuss, Qaenstedt, and P. de Loriol are probably the 

 most striking for details. These represent specimens from the 

 Corallian of Nattheim and Switzerland, which are usually better 

 preserved than those from other localities. 



Distribution. — According to D'Orbigny the species is restricted to 

 the Middle Oolite, having been found in the Callovian of Pizieux, 

 Villers, and St. Scolasse-sur-Sarthe, in France ; Streitberg and Amberg 

 in Germany. It is also recorded from the Corallian of Nattheim in 

 Germany, Switzerland (Bernese Jura), and from similar rocks at 

 Chatel-Censoir, Loix, and lie de Ee in France. Other localities 

 represented by specimens in the British Museum are Viel St. Reine 

 (Corallian) and Vaches Noirs (Oxfordian). We have no record 

 of specimens from the English Oolites. 



Observations on the other Limestone Structures. 



A microscopical examination of Mr. Everett's limestones in the 

 British Museum has led to the following results: — (1) The 

 identification, with Dr. J. W. Gregory's assistance, of the Bx-yozoan 

 genus Heteropora, exhibiting a colony formed of innumerably small 

 zooeciawith faint traces of mesopores, and longitudinally displaying 

 some hoi'izontal tabulge or diaphragms ; in these and other details 

 suggesting a relationship to H. coni/era of Jurassic seas. (2) In the 

 same block of matrix and close to the specimen of Heteropora can 

 be seen the well-defined calices of a coral possessing septa of the 

 hexameral type, and which Dr. Gregory recognizes as Stylina, 

 a genus ranging from Trias to Cretaceous times, with a numerous 

 representation in Oolitic rocks, especially those of Corallian age. 

 (3) A sponge has been determined for me by Dr. G. J. Hinde as be- 

 longing to the group of the Calcispongige and probably to the genus 

 Corynella. The specimen appears to me to resemble some Corallian 

 forms of this genus found in the Nattheim beds of Germany. 



Quite a number of organisms enter into the constitution of these 

 limestones, but they are more or less obscure and difficult to 

 determine ; those referred to on the present occasion are thought 

 to be sufficient for assisting in determining their geological horizon. 



