ON THE CARBONIFEROUS XIPHOSUROUS FAUNA. 145 



tigatious of Dr. Lockwood aud myself, " these forms may iudeed be the huval stages of Prestwi- 

 ohia, Belinurus, etc., the autetypes iu Carboniferous times of the modern kiug crab." " Were it 

 uot for the hirge size of these fossils, some (C. Harl-nestii) measuring five lines in length, three 

 aud one-half lines in breadth, and three lines in height, we should be disposed to agree with 

 Mr. Woodward ; but, from what is known of the size and form of the freshlj-hatched larvse of Lim- 

 ulus and the Trilobites, T should infer that they were either the larva; of some unknown genus of 

 Limulidii?, or adult but embryonic forms. The larvte of Belinurus and its allies, Prestwichia and 

 Euproops, were, in all probability, closely allied in their form and size at the time of hatching to 

 the larva of Limulus. But on comparing the deep hemispherical form of Cyclus, with the surface 

 of the body <leeply lobed over a more or less extent, with the embryo of Limulus before it is 

 hatched. (PI. iv, figs. 18, 18a), we find a striking similarity; indeed, we seem to be dealing with a 

 distinct embryonic type of Limulida*. In Cyclus we have, in a late larval or possibly adult condi- 

 tion, that state of Limulus in which the body is deeply hemispherical, and the abdomen has just 

 been difl:erentiated from the rest of the body, while the deep transverse lobes of the yolk are uot 

 yet absorbed, as seen in PI. iv, figs. 18, 18rt, in the embryo of Limulus ; the cardiac or median lobe 

 being as distinctly marked in Cyclus as in the embryo of Limulus." (DeveloiJuient of Limulus, 

 1872, p. 189.) 



After again reviewing the characters of Cyclus, with the specimen of C, americanus before us, 

 we feel confirmed in the views above presented, and would regard Cyclus as the representative of 

 a family of Xiphosura, being an adult form, and embryotypic, to coin a word, of a Limulus, while 

 the Belinuridse represent the larval Limulus. 



Family DIPELTID^ Packard. 

 DiPELTis DiPLODiscus Packard. PI. V, tigs. -*, 2». 

 Dipeltia diplodisotia Pack., Amer. Naturalist, xix, 293, March, lSf*5. 



This name was proposed for a singular form which is not satisfactorily preserved, so that its 

 exact relations are not readily determinable. The body is suborbicular, flattened, disk-like, slop- 

 ing regularly and gradually from the median area to the edge ; it is divided into two portions ; the 

 larger one to be regarded as anterior or the cephalic shield, and the other as posterior, constituting 

 the abdomen (urosome). The edge of the body is very slightly margiuate, not broadly so as in 

 Cyclus; nor is the body distinctly trilobate, as in the Belinuridie and Limulidse, though unfortu- 

 nately the median area of the cephalic shield is wanting. The integument is rather thin, showing- 

 no traces of segments ; its surface may have had a few scattered small tubercles, at least there are 

 slight indications of them. The surface is smooth and shining. 



The cephalic shield is nearly twice as broad as long ; the posterior lateral angle is well-rounded, 

 with no sign of a lateral spine; in front the edge was probably obtusely rounded; the surface is 

 slightly convex, the disk being low and flat, with no traces of a glabella ; the hind edge of the 

 shield is moderately concave, the limits between it and the urosome being clearly indicated by a 

 slight, but distinct, regular, curvilinear suture. 



The urosome is about three-fourths as long as, but equal in width to the cephalic shield. The 

 front edge is somewhat arcuate, so that the projecting anterior-lateral angle is directed a little 

 forward, and is quite free from the lateral angle of the cephalic shield, which turns away anteriorly 

 from it, leaving a triangular space between the sides of the two regions. Posterior edge of the 

 urosome regularly rounded, and with a slight margin. No traces of a caudal lobe or spine. Total 

 length, 20""" ; total breadth, 20""" ; length of cephalic shield, 11'"™ ; breadth, 20""' ; length of urosome, 

 9°"°; breadth, 19.5""'. Collection of R. D. Lacoe, 2017 "•''•'■ in a nodule from Mazou creek, Morris, 

 Illinois. 



This remarkable animal was disk-like in shape, composed of two regions, the head and abdo- 

 men or urosome, which are more distinctly separated than in the Cyclidte ; while there are no posi- 

 tive characters to separate it from this groujj, we would, for the present at least, refer it to an 

 allied family, as it is orbicular, tailless, aud consists of a broad, large cephalic shield, with a shorter, 

 distinct, non-segmented urosome. 

 S. Mis. 151 19 



