The available specimens of M. smithi differ from all other specimens of a similar total length (6.8-7.2) within the genus by the long skull 7.0-7.6% TL and long lower jaw 11.8-12.5% TL. Furthermore, it is distinguished by the following combination of characters: head long with elongate, pointed snout slightly upturned, rostral fang strongly hooked with distal part in a nearly right angle to dorsal profile of skull, preanal 36.0-37.5% TL, and at least 7 teeth in jaw (Ref. 34506).