_D. valvarum singularum acuminibus superioribus et inferioribus vix intersecantibus: scutorum segmento basali multo angustiore quam segmentum occludens; longitudine ferè dimidiâ: tergis bipenniformibus, margine integro, manubrii acumine ad carinam flexo._ Valves with the upper and lower points of the several valves only just crossing each other. Scuta with the basal segment much narrower than the occludent segment, and about half as long as it. Terga like a battle-axe, with the edge smooth, and the point of the handle bent towards the carina. Mandibles with four teeth; caudal appendages twice as long as the pedicels of the sixth cirrus. Indian Ocean; attached to a sea-snake. This species comes very close to the _D. Grayii_, which likewise was attached to a snake; but I cannot persuade myself, without seeing a graduated series, that the differences immediately to be pointed out can be due to ordinary variation. I am much indebted for specimens to the kindness of Mr. Busk. _General Appearance._--The membrane of the capitulum and peduncle is surprisingly thin and pellucid, so that the ovarian tubes within the peduncle can be traced with the greatest ease. The valves are small, the apices only just crossing each other, and are composed of yellow chitine, with mere traces of calcification. The capitulum is pointed, oval, .15 of an inch long; the peduncle is narrow, and fully twice as long as the capitulum. _Scuta._--The two segments stand at right-angles to each other; the basal segment is linear and pointed, fully half as long, but only one third as wide, as the occludent segment. The point of junction of the two segments is wider than the rest of the basal segment. This latter segment lies some little way above the top of the peduncle. The occludent segment is bluntly pointed; it is directed a little inwards from the edge of the orifice towards the terga; the apex reaches up just above the slightly reflexed lower point of the terga. The adductor muscle is fixed under the point of junction of the two segments. The _Terga_ are battle axe-shaped, with the blade part very prominent, smooth-edged; behind the blade there is a short upwardly-turned prominence. The lower point of the handle of the axe, is bent towards the carina. The tergum, measured in a straight line, equals in length two thirds of the occludent segment of the scutum, the handle being rather narrower than this same segment.