The submicroscopic morphology of magnesian calcite skeletal units of echinoids, revealed by scanning electron microscopy, was compared with crystal orientation data obtained by x-ray methods and with macroscopic morphology. The Perischoechinoidea and the Euechinoidea differ with regard to the shapes of their trabeculae. Nearly all plates and spines are single crystals. A variety of diJfferent d...

in this paper, we investigate various kinds of extensions of twin-good rings. moreover, we prove that every element of an abelian neat ring r is twin-good if and only if r has no factor ring isomorphic to z2  or z3. the main result of [24] states some conditions that any right self-injective ring r is twin-good. we extend this result to any regular baer ring r by proving that every element of a...

Abundant Cardioichnus planus SMITH & CRIMES, 1983 have been reported for the first time from Africa. They occur in lower Miocene deep-marine deposits near Tiaret northwestern Algeria. Morphological features of trace, coupled with spatial interrelationships between and echinoids documented this area, provide evidence that endemic spatangoid Echinocardium nummuliticum PÉRON GAUTHIER, 1885 rep...

Electrophysiological studies in echinoderms are rare. In echinoids investigations have been made by Takahashi and Sandeman. The former used Diadema setosum, the latter Strongylocentrotus, Tripneustes and Toxopneustes. Takahashi gives a brief account of the electrical concomitant of the photic responses already described in detail by Millott and co-workers. Behavioural studies showed that the ra...

Echinoderm genome sequences are a corpus of useful information about a clade of animals that serve as research models in fields ranging from marine ecology to cell and developmental biology. Genomic information from echinoids has contributed to insights into the gene interactions that drive the developmental process at the molecular level. Such insights often rely heavily on genomic information...

in this article we study two different generalizations of von neumann regularity, namely strong topological regularity and weak regularity, in the banach algebra context. we show that both are hereditary properties and under certain assumptions, weak regularity implies strong topological regularity. then we consider strong topological regularity of certain concrete algebras. moreover we obtain ...