4S Mr. Toiilmin Smith on, the Ventriculidse of the Chalk. 
of the minor modifications, will be the better understood from 
the following table of classification, in which I have arranged the 
species belonging to each genus in such relative position as should 
best display the transition from one general character of folding 
to another, and thus gradually realize the true relations existing 
between the very different forms which lie at the two extremes. 
Class MOLLUSCA TUNICATA*. 
Ventriculites, Mant. 
§ a. SiMPLICES. 
1. simplex. 
2. impressus. 
3. quincuncialis. 
4. muiicatus. 
5. tessellatus. 
6. cavatus. 
7. striatus. 
§ h. CoMPLICATI. 
1. mammillaris. 
2. latiplicatus. 
3 decurreiis. 
Far. tenuiplicatus. 
4. radiatus, Mantell. 
5. bicomplicatiis. 
Order Polyzoa 
P’amily Ventriculidse. 
Cephalites. 
§ a. Annulati. 
1. longitudinalis. 
2. guttatus. 
3. paradoxus. 
4. alternans. 
5. biillatus. 
6. retrusus. 
7. cateiiifer. 
Far. annulatus. 
8. compressus. 
§ h. Dilatati. 
1. capitatus. 
2. campanulatus. 
3. constrictus, 
4. perforatus. 
Brachiolites. 
§ a. Operti. 
1. tuberosus. 
2. elegaiis. 
3. convolutus. 
4. angularis. 
§ b. Aperti. 
1. foliaceus. 
2. racemosus. 
3. digitatus. 
4. tubulatus. 
b. fenestratus. 
6. labrosus. 
7. protensus. 
* It is quite be^mnd my present purpose to discuss the exact position of 
the Polyzoa. The main truth of Professor E. Forbes’s opinion is however 
so generally recognized, that I am justified in the above designation of class, 
which must always be felt to be an important element in giving vitality to 
a classification. Professor Forbes says, ‘'The anatomical structure of the 
Ascidioida or Bryozoa removes them altogether from the class of Zoophyta 
into that ofMollusca, where they should form an order of Mollusca tunicata 
parallel with the group of compound Tunicata of which Botryllus and such 
forms are examples.” — Ann. and Mag. of Nat. Hist. vol. xiv. p. 390. See 
Owen’s Lect. on Corap. Anat. I. pp. 100 and 269, 270 ; Van Beneden, Re- 
cherches sur les Bryozaires, p. 37 ; Johnston’s British Zoophytes, p. 2. 
(See also Thompson and Farre.) The actual and important distinctions are 
noticed by the last writer, p. 256 ; and the vast superiority in vital activity 
of the Polyzoa to the Ascidians, is well pointed out by Sir J. G. Dalyell (ut 
ante) pp. 229, 230. I have heretofore used the general terra “ zoophytes ” 
in conformity, as already intimated (vol. xx. p. 190), to what is at present 
the ordinary language of authors, and a departure from which would, 
therefore, have caused ambiguity and unnecessary confusion. 
T Thompson', Bryozoa, Ehrcnherg-, Ciliobrachiata, Farre. 
[To be continued.] 
