_Anomalies._--There is a high incidence of anomaly in the type series. Three of the specimens (USNM 60976, IU 42954, and KU 39415) have a supernumerary central lamina. All of the specimens from Durango are anomalous in regard to the marginal laminae. In the holotype the first marginals are small, approximately as wide as the small precentral. In the largest paratype (USNM 61254) the first and second marginals are fused to form a single large scute on each side. In the remaining Durangan paratype (USNM 60976) there are eleven normal marginals on each side but a supernumerary lamina occurs between the first and second marginal on the left and between the precentral and first marginal on the right side. The remaining three paratypes have the number of marginals that is normal for the genus. _Relationships._--_Gopherus flavomarginatus_ differs from all other species of the genus by its larger size and by having an intergular seam that is longer than the interhumeral seam. The possession of a single, rectangular axillary scale, wider below than above, also tends to distinguish _flavomarginatus_ from other living _Gopherus_; in the other species this scute (frequently paired in _berlandieri_) is generally triangular or at least pointed below. Femoral spurs are developed to varying degrees in the other species of _Gopherus_; they are usually lacking in individuals of small to medium size. In large specimens of _agassizii_ and _polyphemus_ that I have examined, there is but one enlarged spur, although several pointed osteodermal scales may be present on the back of the thigh. _Gopherus berlandieri_, the closest relative of _G. flavomarginatus_ in a geographic sense, has a highly arched shell and pronglike gular projections, between which there is nearly always a deep notch. _Gopherus agassizii_, morphologically the closest Mexican relative of _flavomarginatus_, differs from it in having a narrower head and in lacking the contrasting pale and dark coloration of the plastron and lateral marginal area. _Gopherus polyphemus_ seems to be the closest relative of _flavomarginatus_ and differs from it in having an unflared shell (anterior and posterior widths of carapace subequal or carapace narrower behind) and in the characteristics of color mentioned above. Certain proportional differences between the living species of _Gopherus_ are summarized in table 2.