446 Annals New York Academy of Sciences 



kiminaled algal-mats such as can be observed forming today at Turner and 

 Price Falls, Oklahoma, or equivalent forms described by Black from the 

 mudtlats of Andros Island, Bahama; domes, heads, and more extensive digitate 

 masses. Onkolites (unattached forms) can have the shape of the nucleus or 

 be variously shaped biscuits or flattened discs. '^'' 



Factors such as a slight increase in iron above tolerance amounts have long 

 been known to retard growth, affect size, and ultimately, the shape of several 

 nonmarine, nonlime secreting, filamentous algae.'"^ Cyclicity in occurrence of 

 the Cambrian form Cryptozoon nndulatum was attributed to inhibition of 

 growth due to increasing turbidity caused by transported sediments.'^- Pre- 

 Cambrian bioherms of Northwestern Montana show different forms — columns, 

 domes, sheets — which were "apparently" determined by physical conditions 

 such as water movements.''^ The ultimate external form of Recent algal bis- 

 cuits is credited to two determinants: stability of the surface on which the 

 biscuits grow and the strength of attachment to it.*^^ 



Work in progress (Tasch, unpublished) on newly discovered algal reefs and 

 onkolites in the Kansas Permian provide some evidence on controls of ultimate 

 form. An influx of mud over the growing algal mat (stromatolite) inhibited 

 growth in certain directions only. Turbidity, of course, can exclude or diminish 

 hght penetration and hence interfere with photosynthesis. If, however, sedi- 

 ment influx is negligible (4 to 5 mm.), filamentous algae can "move up through 

 the sediment and reestablish themselves on the surface. '"^^ The topography 

 of the substrate on which the original filamentous algal mat spread, also can 

 be a partial determinant of shape of a stromatolite. 



Sporadic circular to elliptical perforations of algal blades in the fossil genus 

 Eugenophyllum appear to represent adaptive modifications. Although these 

 forms lived below normal wave agitation, the perforations would help to dissi- 

 pate even gentle current action against the upright blades which are several 

 inches in height.''" 



Among factors influencing growth of stromatolites and onkolites are: sub- 

 strate, turbidity, amount of light penetration, depth of water, wave and current 

 action. Influence of metallic cations can also be inferred. 



. Terrestrial M icroproblemal ica 



Microproblematica are apparent fossils observed in sections of rock suffi- 

 ciently thin to transmit light. They are primarily of Mesozoic age, but are 

 also known from the Paleozoic and Pre-Cambrian. Distinctive structure and 

 form characterize them. However, they cannot confidently be assigned to 

 any known taxa. Occasionally, additional study and collection permits ulti- 

 mate resolution of assignment.^' •'"- 



The microfossil Xamioconus kanipliicr, 1931, is a good example. The object 

 ranges from 5 to 50 /u in length, with an average of 15 to 20 fx; width varies 

 from 5 to 15 /x. It is definitely an "organized object." There is a distinctive 

 wall composition (spirally arranged calcite wedges, 1 m in thickness). In 

 longitudinal section, it is either conical, spherical, barrel-, or pear-shaped, or 

 cylindrical U-shaped. There is an axial canal or a basal cavity, or both, and 

 2 apertures opposite each other. Through time, it shows apparent speciation.''* 



Nannoconus is widespread in distribution, having been reported from the 



