The answer.

[tlford@ix.netcom.com (Tracy Ford)]

I've waited to see if anyone else would answer my test question.
(which only two people did). I guess no one else wanted to know :->

Anyway here is my answer to my question.

I'll be quoting from several of SEELEY's papers.

>From what I can tell, the only reason H. G. Seeley placed the 
Sauropoda within the Saurischia which had the Theropoda
already in it, was because of the pneumatic bones the Sauropoda 
had. The pneumatic bones was similar to the pneumatic bones 
of the theropoda. That is the only reason that I've been able to find, 
why he placed the Sauropoda in the Saurischia. It had nothing to do
with the pelvis, or should I say it seemed to be less about the pelvis 
than the pneumatic vertebrae.

Seeley, H. G. 1888. On Thecospondylus davisei, Seeley, with some 
remarks on the Classification of the Dinosauria. 
Quart. Jour. Geol. Soc. London, LXIV: 79-87.

p. 85, last paragraph.

"At the time, Hypsilophodon, Iguanodon, Hadrosaurus, and Scelidosaurus 
gave the best conception of the Dinosauria. It has been the fortune of 
others  to elaborate the group thus indicated. Mr. Hulke has admirably 
described Ornithopsis, and Professors Cope, Huxley, and Marsh have 
investigated the structure of its allies, and their classification. But 
it has seemed to me that the classifictional value of the pneumatic 
skeleton has been underestimated in the results which have been 
formulated. Professor Marsh has been led to form an order of animals 
for the type to which Ornithopsis belongs. This order was named 
Sauropoda, and has for it's European types Cetiosaurus and 
Ornithopsis."

p. 86.

"As early as December 1874 I suggested the name Cetiosauria as an 
ordinal division of the Dinosauria, and therefore am in harmony with 
Professor Marsh in Separating these types from the remainder of the 
Dinosauria, though the separation may be based upon different data form 
those adopted by Professor Marsh. These animals are characterized by 
pneumatic vertebra."

No mention of the pelvis. It continues.."And therefore when and 
additional order is instituted for animals with cavernous or pneumatic 
vertebrae, the Theropoda of Marsh, under which Coelurus is grouped, it 
becomes necessary, in order to determine the systematic position of 
Thecospondylus, to briefly review its relations to allied animals. I 
have no doubt that the two ordinal groups, Sauropoda and Theropoda 
should be united into one order, the Saurischia, while the Stegosauria 
and Ornithopoda should be united into and order, the Ornithischia."

It's more clear in the following summery.

Seeley, H. G. 1888. On Thecospondylus davisei, Seeley, with some 
Remarks on the Classification of the Dinosauria. Geol. Mag. (3) V: 45.

Last paragraph;

"Professor Marsh has formed an Order, Sauropoda, which includes 
Cetiosaurus and Ornithopsis. The author remarks that he had already  
suggest Cetiosauria as separable from the rest of the Dinosaurs. When 
an additional Order is institued for animals with cavernous or 
pneumatic vertebrae, the Theropoda of Marsh, under which Coelurus is 
grouped, it becomes necessary, in order to determine the systematic 
position of Thecospondylus, to review its relations. The author would 
unite Sauropoda with Theropoda into one Order, the Saurischia, whose 
pneumatic skeleton is an approximation towards Ornithosaurs and 
birds.""

Again just the pneumatic vertebrae.

Ok, so after reading Seeley, 1887 last I see I may be wrong in my 
thinking.  

Seeley, H. G. 1887. On the Classification of the Fossil Animals 
commonly named Dinosauria. Proc. Roy. Soc. London, Vol. XLIII: 165-171.

He does state on page 167, half way down the page..: "The characters on 
which these animals should be classified are, I submit, those which 
pervade the several parts of the skeleton, and exhibit some diversity 
among the associated animal types. The pelvis is perhaps the more 
typical of these animals than any other part of the skeleton, and 
should be a prime element in classification. The presence or absences 
of the pneumatic condition of the vertebrae is an important structural 
differences."

Then he goes into the pelvis and again about the pneumatic vertebrae. 

It just seemed to me, in reading the two first articles, he was really 
relying on the pneumatic vertebrae and not the pelvis. Why he didn't go 
into the pelvis in these papers I don't know. 

So the answer is?The pelvis, and more importantly (at least that is how 
I reed what Seeley wrote) the pneumatic vertebrae.

Tracy