C. Lapworth—Recent Discoveries in Sweden. 69 
indeed any of the local geologists, have ever been able to detect a 
fragment of JIL priodon in the Lower Ludlow rocks. A glance at 
Sowerby’s drawing of the species in question (Siluria, plate xviii. 
fig. 1a), shows that it was made from a partly-decorticated specimen. 
His magnified drawing, fig. 1a, certainly gives the general impression 
that the thecz were similar in form to those of J priodon. But it is 
impossible to reconcile their appearance with that of the thece on 
the adult part of the polypary on fig. 1, which are like those of my 
M. M‘Coyii. If the examples illustrated on fig. 2 are the same 
Species, the question is settled, for these are wholly distinct from 
those of M. priodon. As regards If. Clintonensis, Hall, the differences 
are so marked that the question of identity may soon be disposed of. 
In JL Clintonensis, Hall, the polypary is slender; it has a ventral 
curvature; its proximal thecz are those of the proximal end of JL 
Sedgwicki, Portk. (var. Heuberni, Geinitz) ; its distal thecee alone re- 
semble those of JZ. priodon, and they are wholly destitute of anything 
like overlap. In JL. priodon, on the other hand, the polypary rapidly 
becomes stout and thick; it is either quite straight, or it has a dorsal 
curvature only; its proximal thecz point in the direction of those of 
MW. lobiferus, M‘Coy ; and in the adult thece there is invariably an 
amount of overlap, equal to at least half the length of the thece. 
Of course, the value of these criteria vary in the minds of paleonto- 
logists in direct proportion to their ideas of what amount of dif- 
ference ought to separate allied species; but I would diffidently 
submit the opinion, that if these three forms had been Trilobites, 
Mr. Linnarsson would never have been aware of the possible exist- 
ence of this difficulty. 
The second form noticed is Retiolites Geinitzianus, Barr. This is 
also illustrated with several fine figures and described with great 
care. rom a comparison of specimens collected, not only from 
Gothland, but also from the mainland of Sweden, and from Norway, 
the author finds the transverse section of the polypary to have been 
an oval, truncated at both ends. He is unable to detect anything 
like true partition-walls—the coarse filaments generally so called 
apparently forming an integral portion of the filiform framework. 
The appearances point rather iu the direction of the theory that the 
whole interior of the polypary formed a single undivided chamber ; 
a theory which, however, he does not advocate, as it is discordant 
with the opinions of those paleontologists who have already carefully 
examined the species. In a specimen in relief, from Norway, he 
finds a sub-median network, like that upon the exterior surface, 
traversing the body of the polypary longitudinally. There is no 
trace of a virgula in the Gothland specimen; but in examples from 
the mainland, a longitudinal fibre is frequently visible ; but whether 
this is actually a true virgula, or whether, as Hall and myself have 
suggested, there are actually two of these median threads, one 
straight and the other zig-zag, there is in the Swedish specimens no 
evidence to show. The mouths of the thece are figured as octagonal, 
but there is no trace of ornamentation around their apertures. 
These Graptolites are found in the strata of both of the two main 
