The principle grades are: gem, fine, good, and fair. "Gem" means an absolutely perfect specimen, flawless to the unaided eye. (The whole shell grading system is based on perceptions of "the unaided eye". With a microscope you can find a microscopic flaw on just about any shell, including "gem" specimens.) "Fine" indicates a shell with a rather obvious flaw, which still does not detract greatly from the overall aesthetic or scientific value of the specimen. "Good" indicates a rather severe flaw or several lesser flaws, which does seriously compromise the appearance and/or scientific value of the specimen. "Fair" indicates a shell which no collector is likely to want in the collection, but which still could have some scientific value if it is very rare. A plus sign (+) is used to designate a grade intermediate between the major grades. For example, "fine+" means better than fine, but still not gem. "Fine++" is often used to designate "virtually, but not quite gem". Careful closeup examination of the specimen is required to discover the flaw on a fine++ specimen. Further information can be found here: http://coa.acnatsci.org/conchnet/grad2faq.html

The name of a species consists of two latin or latinized words - the genus name (Cypraea), which is always capitalized and always a noun, and the specific name (achatidea), which is not capitalized and is often an adjective modifying the genus name. However, the specific name may also have several other configurations. The binomial name of a species is followed by the surname of the person or persons who originally described the species, and the year it was described.
(Answer by M. Paul Monfils via the Forum)

For a new species to be recognized, its description must be published in an accredited publication. "Hwass, in Bruguiere, 1792" means that Hwass first described the species and assigned its name, but his description was first published in a paper written by Bruguiere who, in that paper, identified Hwass as the author of the species description.
(Answer by M. Paul Monfils via the Forum)

If you are collecting beach shells of course it really doesn't matter. The same shells will be lying there day or night. But if you are collecting live specimens, many species are active at night that are hidden during the daytime. Such species can often be found during the day by turning over rocks, sifting sand, etc., but at night many such species are actively crawling around and easier to see. Other species are plainly visible both day and night.
(Answer by M. Paul Monfils via the Forum)

Effectively, most of seashells go out at night. I noticed that they are mostly active just after the sunset. They do not hunt the whole night (too dangerous) and if they find their prey they go back to their hiding place. I studied them in live and in aquarium. In France, with the cowries, as soon as I turned light off, they were looking for their sponges...

Some species may also be active during daytime too. And shells usually do not go out at night when the moon is full. So the worst days are the ones when the moon is gonna be full. As soon as it decrease to be dark they are active again.

I noticed that when moon is in it's full period shells may go hunting during daytime too (too angry I guess...) and so do not wait dark moon period...
(Answer by M. David Touitou via the Forum)