Another 1804 Half Cent

1804 C-5 R-4 Die State IV possibly a little later. This is the first "Spiked Chin" variety but the spike is not showing strongly. (There are four spiked chin varieties plus C-3. C-3 and C-5 are actually the same variety from before and after the damage to the die which created the spiked chin.)

my book calls it a E-42 (G-11) and calls it a R-6. here is what it says about it:
Obv: With spiked chin as on E-38,39 and 40.
Rev: same as E-41. usually seen with a long die crack from A in STATES to wreath, L in HALF, T in CENT and C in AMERICA. Crack also through all bases of letters in legend ICA. Rare in top condition

the book is "United States Half Cents 1793-1857" by Q. David Bowers and James F Ruddy

Yes, The C numbers are Cohen numbers which are the most commonly used system today (1971 on). The G numbers are Gilbert numbers from back around 1916 and were the standard numbers used until the Cohen numbers. The E numbers are Empire numbers, a system devised by Q David Bowers and James Ruddy back in the early 60's when they were running Empire Coin Company. No one ever really used E numbers except Empire.