I have just checked the 1881 census and it shows: 
William SNELL    M     Male  47     Caerleon, Monmouth, England  Pesway Railway Inspector      
 Ann SNELL     Wife     M     Female     46     Eglwysilan, Glamorgan, Wales           
 John SNELL     Son     U     Male     21     Llanfabon, Glamorgan, Wales     Railway Station Master      
 Henry SNELL     Son     U     Male     19     Llanfabon, Glamorgan, Wales     Railway Plate Layer      
 Thomas SNELL     Son          Male     14     Llanfabon, Glamorgan, Wales     Scholar      
 Mary SNELL     Daur          Female     11     Gelygaer, Glamorgan, Wales     Scholar      
 David C. SNELL     Son          Male     5     Gellygaer, Glamorgan, Wales     Scholar      
 Mary F. BOWEN     Serv     U     Female     18     Llantrisant, Glamorgan, Wales     General Serv ,
but I am now intrigued because the Bible entries do not show a Thomas (c 1867) at all! It has got: 
John  b.15th July 1859
Henry  b.16th April 1861
Margret Ann  b.13th Aug 1865    d.1st Nov 1863
Lewis   b. 1st Oct 1864
James   b.21st Jan 1869
A Mary  b. 27th Nov 1869
Sarah   b. 9th Feb 1872          d. 9th April 1873
William  b. 12th Sept 1874      d. 5th Oct 1874 
David Charles   b. 27th Nov 1875
so I wonder what happened to Lewis and where did Thomas come from - possible he was Lewis Thomas I suppose, but William's entry does not show a 2nd name.
Regards
Sue