We show that every primary lattice can be considered a glueing of intervals having geometric dimension at least 3 and with a skeleton of breadth at most 2. We call this geometric decomposition. In the Arguesian case, we analyse the sub-glueings corresponding to cover preserving sublattices of the skeleton which are 2-element chains or a direct product of 2 such. We show that these admit a cover...

Let k be an algebraically closed field, let R be an associative kalgebra, and let F = {Mα : α ∈ I} be a family of orthogonal points in Mod(R) such that EndR(Mα) ∼= k for all α ∈ I. Then Mod(F), the minimal full subcategory of Mod(R) which contains F and is closed under extensions, is a full exact Abelian sub-category of Mod(R) and a length category in the sense of Gabriel [8]. In this paper, we...

The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral regio...