The dental formula of Histriophoca fasciata is: I 3/2, C 1/1, PC 5 (rarely 6) = 34 to 36. The teeth are rather weak, smooth and distantly spaced. The lower incisors are only half the size of the upper ones and are frequently lost. The lower canines point outward at an angle of 45° from the horizontal. In each half of the jaw, upper and lower No. 1 is the smallest of the postcanine series; Nos. 3 and 4 are the largest; Nos. 2 and 5 are nearly equal. On some skulls the gap between upper postcanines Nos. 4 and 5 is distinctly the widest. The upper postcanines may have a small posterior cusp; the lower ones frequently have both anterior and posterior cusps. In each half of the jaw, upper and lower postcanine No. 1 is single rooted; No. 5 is double rooted; Nos. 2, 3 and 4 are transitional.

On one specimen, the third pair of upper postcanines is missing and all of the teeth are unusually small. This skull may be pathological or it may be evidence of the variation to be expected in a declining evolutionary form.

Male and female are similar in body size and may reach a length of at least 170 cm. and a weight of at least 95 kg. Cranial measurements of five adult males, one adult female and one adult sex-unknown are given.