We model anomalies in wireless sensor networks with ellipsoids that represent node measurements. Elliptical anomalies (EAs) are level sets of ellipsoids, and classify them as type 1, type 2 and higher order anomalies. Three measures of (dis)similarity between pairs of ellipsoids convert model ellipsoids into dissimilarity data. Clusters in the dissimilarity data may correspond to normal and anomalous measurements and nodes in the network. Assessment of (clustering) tendency is facilitated by visual inspection of (VAT/iVAT) images. Two examples illustrate the potential for anomaly detection.