a new species of cassiduloid echinoids, pygaulus baghinensis is reported for the first time from aptian sediments of baghin area, west of kerman, iran. the diagnostic features of the species are centrally positioned of the apical disc and approximately low profile of the test. variation in gonopore size in different individuals allows to conclude that p. baghinensis is sexually dimorphic. speci...

the spatangoid genus schizaster agassiz is recorded, for the first time, from the lutetian (middle eocene) deposits of sargaz area, south of kerman, iran. the lutetian sediments of sargaz region contain a rich and divers echinoid fauna represented by cidaridae, conoclypeidae, echinolampadidae, toxopneustidae, phymosomatidae and schizasteridae. schizasteroid echinoids are an important component ...

abderaz formation is one of the upper cretaceous formations in the kopet-dagh sedimentary basin. a stratigraphic section from the mentioned formation is selected for detailed systematic description with regard to echinoids. numerous well preserved representatives of the families mircrasteridae wright, 1857 and echinocorythidae lambert, 1920 are described from the ghaleh-zoo stratigraphic sectio...

r is called commuting regular ring (resp. semigroup) if for each x,y $in$ r thereexists a $in$ r such that xy = yxayx. in this paper, we introduce the concept of commuting$pi$-regular rings (resp. semigroups) and study various properties of them.

two new species of an arbacioid echinoid, genus goniopygus, are reported for the first time from aptiansediments of baghin area, kerman, iran. the main features of the species lie in apical disc and peristomediameter. in goniopygus triangularis sp. nov., the periperoct is triangular in shape with three small, sunkentubercles, located alternatively adjacent to the periperoct, while goniopygus an...

Heterochrony has become a central organizing concept relating development and evolution. Unfortunately, the standard definition of heterochrony--evolutionary change in the rate or timing of developmental processes--is so broad as to apply to any case of phenotypic evolution. Conversely, the standard classes of heterochrony only accurately describe a small subset of the possible ways that ontoge...