The most common design of bubby pot (a.k.a. "suckling pot") is pictured at left. It was designed by Dr. Hugh Smith around 1770 to be an improvement over the other artifical designs of the period (primarily ceramic feeding bottles). The name "bubby" was derived from an old world euphemism for female breast and the most unique unique design attributes were its lid's small air hole for flow regulation and the spout perforated spout tip.
I understand that Dr. Smith's first prototype was made of pewter (see silver example below) and quickly afterword other design variations come out also using perforated spout openings.
Now the bad news, the bubby pot's design (with its impossible to clean spout and basically closed but perforated spout end) significantly contributed to infant mortality. This sad historical fact, coupled with the ceramic version's extremely delicate and small nature explains their rarity.
An interesting comparison of an illustrated bubby pot with its original -
One comes across ceramic pots and/or cups similar to those at left and lower left when collecting.
To me the distinction between them is whether or not they have a perforated spout tip. If they do I consider them to be suckling pots and if they don't I consider them to be feeding cups.
Similar designed suckling pots also came in silver and pewter (see photo below).
This is a wonderful example of a transfer-printed suckling pot with its contents regulated similar to feeding bottles (i.e., placing a thumb over the top).
This design of pot was also made in silver and pewter (see photos below) except their spout tips were a single hole as opposed to perforated with many small holes.
Not to get to far off subject it is interesting to note that in many silver suckling pot designs they come with built-in filtration traps, unlike their ceramic cousins (see photos below).
Examples of other shaped and sized pots: