Diversity

Lachnopus is currently placed in the tribe Geonemini Gistel, according to Alonso-Zarazaga & Lyal, 1999). With 66 described species and several additional species waiting to be described, it constitutes the most diverse and widespread genus of Caribbean borad-nosed weevils.
Until now Lachnopus ranges from the south-eastern United States to Saint Vincent in the Lesser Antilles, with the highest species diversity concentrated in the Greater Antilles; most of Lachnopus species are apparently narrowly distributed and exhibit high rates of inter and/or intra-island endemism (see O’Brien and Wibmer 1982).
The species currently placed in the genus are extremely variable:

• Size ranging from 5 to 25 mm
• Body shapes ranging from elongate to oval
• Integument and scale color
• Wide spectrum of scale distribution patterns

According to van Emden’s Key (1944) Lachnopus can be recognized by a rostrum weakly and evenly convex throughout; antennal scape extending to, or slightly passing beyond middle of eye; frons between eyes conspicuously narrower than dorsal surface of rostrum; head not constricted posteriad of eyes; eyes only moderately convex; humeri only slightly wider than posterior margin of pronotum; femora unarmed; tibiae ventrally denticulate; and metatibial corbel (bevel sensu Thompson 1992) lacking scales. BUT, based only on the frons width, you can tell that not all species fit in van Emden's definition.

From left to right: top row: L. valgus, L. aurifer, L. planifrons and L. histrio; bottom row: L. albomaculatus, L. campechianus and L. acuticollis.

With so much variation within the same genus, it seems to me that Lachnopus has been the "trash-can" of Caribbean entimines for a long time. In fact, Woodruff (1985: 371) used one of my favorite phrases in weevil's literature to describe Caribbean diversity: 'a ‘Pandora’s Box of taxonomic confusion'.
The same happens for the whole tribe (I will tell you later why).

References
     Alonso-Zarazaga, M. A., and Lyal, C. H. C. (1999). ‘A World Catalogue of Families and Genera of Curculionoidea (Insecta: Coleoptera) (Excepting Scolytidae and Platypodidae).’ (Entomopraxis: Barcelona, Spain.)
     O’Brien, C. W., and Wibmer, G. J. (1982). Annotated checklist of the weevils (Curculionidae sensu lato) of North America, Central America, and the West Indies (Coleoptera: Curculionoidea). Memoirs of the American Entomological Institute 34, 1–382.
     van Emden, F. (1944). A key to genera of Brachyderinae of the World. Annals & Magazine of Natural History 11(XI), 503–532, 559–586.
     Thompson, R. T. (1992). Observations on the morphology and classification of weevils (Coleoptera, Curculionoidea) with a key to major groups. Journal of Natural History 26, 835–891.
     Woodruff, R. E. (1985). Citrus weevils in Florida and the West Indies: preliminary report on systematics, biology and distribution (Coleoptera: Curculionidae). The Florida Entomologist 68, 370–379.